feat: Plugin-System Umbau — 6 Phasen komplett abgeschlossen

Phase 1: Contracts konsequent nutzen
- 12 neue contracts.py erstellt (alle 19 Plugins haben jetzt contracts)
- 4 bestehende contracts.py an zentrale ContractRegistry angepasst
- Alle 19 Plugins haben on_deactivate mit Contract-Unregister
- 0 echte problematische INTER-Plugin Imports

Phase 2: Hooks/Filters-System
- app/core/hooks.py (HookRegistry mit actions + filters)
- 15 Hook-Punkte in Core-Services (contact, auth, mail, calendar, user, dms)
- BasePlugin.on_deactivate meldet alle Hooks ab

Phase 3: Plugin-Isolation
- scripts/check_cross_plugin_imports.py (Linting-Regel)
- .github/workflows/check-cross-plugin-imports.yml (CI/CD)
- .pre-commit-cross-plugin.yaml (Pre-commit Hook)
- 155 Dateien geprueft, 0 Verstoesse

Phase 4: Plugin-Versioning
- app/plugins/semver.py (SemVer mit Parse, Compare, Pre-release)
- migration_runner.py erweitert: run_migration_down, rollback_to_version
- manifest.py: min_app_version Feld
- registry.py: App-Version-Compatibility-Check bei Installation
- GET /api/v1/plugins/updates Endpoint

Phase 5: Marketplace-Vorbereitung
- app/plugins/signature.py (Ed25519 Signatur-Validierung)
- app/plugins/quarantine.py (Plugin-Quarantine mit Validierung)
- app/models/plugin_allowlist.py + Migration 0046
- manifest.py: author, license, homepage, icon, screenshots, changelog, marketplace_tags, price
- registry.py: discover_external(), discover_all()
- POST /api/v1/plugins/install-marketplace (deaktiviert)

Phase 6: Manifest-Anpassung
- manifest.py: 12 neue Felder + SemVer/Hook-Name Validierung
- MANIFEST_SCHEMA_DOC aktualisiert
- Alle 19 Plugin-Manifeste aktualisiert
- Frontend PluginUiManifest Typ erweitert

Zusaetzliche Bug-Fixes:
- test_sample-Modul erstellt
- conftest.py Deadlock-Prevention
- SESSION_COOKIE_SECURE=true
- dump.rdb aus Git entfernt + .gitignore
- backup.py datetime.utcnow -> func.now()
- system_settings.py JSONB-Import nach oben
- tax.py Mapped[float] -> Mapped[Decimal]
- notification.py type_key-Laengen vereinheitlicht

Tests: 91 neue Tests, alle bestanden

tests/test_hooks.py

@@ -0,0 +1,194 @@
+"""Tests for the WordPress-style hooks/filters system."""
+
+from __future__ import annotations
+
+import asyncio
+import pytest
+
+from app.core.hooks import (
+    HookRegistry,
+    get_hook_registry,
+    do_action,
+    apply_filters,
+    reset_hook_registry_for_testing,
+)
+
+
+@pytest.fixture(autouse=True)
+def clean_registry():
+    """Reset the hook registry before each test."""
+    reset_hook_registry_for_testing()
+    yield
+    reset_hook_registry_for_testing()
+
+
+class TestHookRegistry:
+    def test_singleton_identity(self):
+        """HookRegistry is a singleton."""
+        reg1 = get_hook_registry()
+        reg2 = get_hook_registry()
+        assert reg1 is reg2
+
+    def test_register_action(self):
+        """Actions can be registered and listed."""
+        reg = get_hook_registry()
+        called = []
+        reg.register_action("test.action", lambda: called.append(True))
+        assert reg.has_action("test.action")
+        assert "test.action" in reg.list_actions()
+
+    def test_register_filter(self):
+        """Filters can be registered and listed."""
+        reg = get_hook_registry()
+        reg.register_filter("test.filter", lambda v: v + "!")
+        assert reg.has_filter("test.filter")
+        assert "test.filter" in reg.list_filters()
+
+    @pytest.mark.asyncio
+    async def test_do_action_calls_callback(self):
+        """do_action executes registered callbacks."""
+        reg = get_hook_registry()
+        called = []
+        reg.register_action("test.action", lambda: called.append("yes"))
+        await do_action("test.action")
+        assert called == ["yes"]
+
+    @pytest.mark.asyncio
+    async def test_do_action_with_args(self):
+        """do_action passes arguments to callbacks."""
+        reg = get_hook_registry()
+        received = []
+        reg.register_action("test.action", lambda x, y: received.append((x, y)))
+        await do_action("test.action", 1, 2)
+        assert received == [(1, 2)]
+
+    @pytest.mark.asyncio
+    async def test_do_action_async_callback(self):
+        """do_action supports async callbacks."""
+        reg = get_hook_registry()
+        called = []
+
+        async def async_cb():
+            called.append("async")
+
+        reg.register_action("test.action", async_cb)
+        await do_action("test.action")
+        assert called == ["async"]
+
+    @pytest.mark.asyncio
+    async def test_do_action_priority_order(self):
+        """Actions execute in priority order (lower first)."""
+        reg = get_hook_registry()
+        order = []
+        reg.register_action("test.action", lambda: order.append("low"), priority=20)
+        reg.register_action("test.action", lambda: order.append("high"), priority=5)
+        reg.register_action("test.action", lambda: order.append("mid"), priority=10)
+        await do_action("test.action")
+        assert order == ["high", "mid", "low"]
+
+    @pytest.mark.asyncio
+    async def test_do_action_no_callbacks(self):
+        """do_action with no registered callbacks does nothing."""
+        await do_action("nonexistent.action")
+
+    @pytest.mark.asyncio
+    async def test_do_action_swallows_exceptions(self):
+        """do_action logs but does not raise on callback errors."""
+        reg = get_hook_registry()
+        called = []
+        reg.register_action("test.action", lambda: (_ for _ in ()).throw(ValueError("boom")))
+        reg.register_action("test.action", lambda: called.append("after_error"))
+        await do_action("test.action")
+        assert called == ["after_error"]
+
+    @pytest.mark.asyncio
+    async def test_apply_filters_modifies_value(self):
+        """apply_filters passes value through callbacks."""
+        reg = get_hook_registry()
+        reg.register_filter("test.filter", lambda v: v.upper())
+        result = await apply_filters("test.filter", "hello")
+        assert result == "HELLO"
+
+    @pytest.mark.asyncio
+    async def test_apply_filters_chains_multiple(self):
+        """apply_filters chains multiple callbacks in priority order."""
+        reg = get_hook_registry()
+        reg.register_filter("test.filter", lambda v: v + " B", priority=20)
+        reg.register_filter("test.filter", lambda v: v + " A", priority=10)
+        result = await apply_filters("test.filter", "start")
+        assert result == "start A B"
+
+    @pytest.mark.asyncio
+    async def test_apply_filters_no_callbacks(self):
+        """apply_filters with no callbacks returns original value."""
+        result = await apply_filters("nonexistent.filter", "original")
+        assert result == "original"
+
+    @pytest.mark.asyncio
+    async def test_apply_filters_async_callback(self):
+        """apply_filters supports async callbacks."""
+        reg = get_hook_registry()
+
+        async def async_upper(v: str) -> str:
+            return v.upper()
+
+        reg.register_filter("test.filter", async_upper)
+        result = await apply_filters("test.filter", "hello")
+        assert result == "HELLO"
+
+    def test_unregister_specific_callback(self):
+        """unregister removes a specific callback."""
+        reg = get_hook_registry()
+        cb1 = lambda: None
+        cb2 = lambda: None
+        reg.register_action("test.action", cb1)
+        reg.register_action("test.action", cb2)
+        assert reg.has_action("test.action")
+        reg.unregister("test.action", cb1)
+        assert reg.has_action("test.action")
+        reg.unregister("test.action", cb2)
+        assert not reg.has_action("test.action")
+
+    def test_unregister_all_for_plugin(self):
+        """unregister_all_for_plugin removes hooks owned by a plugin instance."""
+        reg = get_hook_registry()
+
+        class FakePlugin:
+            class manifest:
+                name = "fake_plugin"
+
+            def __init__(self):
+                self.manifest = type("m", (), {"name": "fake_plugin"})()
+
+            def my_action(self):
+                pass
+
+            def my_filter(self, v):
+                return v
+        plugin = FakePlugin()
+        reg.register_action("test.action", plugin.my_action)
+        reg.register_filter("test.filter", plugin.my_filter)
+        assert reg.has_action("test.action")
+        assert reg.has_filter("test.filter")
+        reg.unregister_all_for_plugin("fake_plugin")
+        assert not reg.has_action("test.action")
+        assert not reg.has_filter("test.filter")
+
+    @pytest.mark.asyncio
+    async def test_apply_filters_swallows_exceptions(self):
+        """apply_filters logs but does not raise on callback errors."""
+        reg = get_hook_registry()
+        reg.register_filter("test.filter", lambda v: (_ for _ in ()).throw(ValueError("boom")))
+        reg.register_filter("test.filter", lambda v: v + "!")
+        result = await apply_filters("test.filter", "test")
+        # First filter errored, second still ran
+        assert result == "test!"
+
+    def test_reset_for_testing(self):
+        """_reset_for_testing clears all state."""
+        reg = get_hook_registry()
+        reg.register_action("test.action", lambda: None)
+        reg.register_filter("test.filter", lambda v: v)
+        reg._reset_for_testing()
+        assert not reg.list_actions()
+        assert not reg.list_filters()