T03: plugin system framework + lifecycle + migrations + event bus + DI

- Plugin registry with discover/install/activate/deactivate/uninstall lifecycle
- PluginManifest Pydantic v2 schema (name, version, dependencies, routes, events, migrations)
- BasePlugin abstract class with lifecycle hooks (on_install/activate/deactivate/uninstall)
- Migration runner with tenant_id validator (rejects tables without tenant_id)
- Event bus integration: register/unregister listeners on activate/deactivate
- Service container DI: plugins receive db, cache, event_bus, storage, notifications
- Idempotent operations (activate active=200, deactivate inactive=200)
- UI registry for frontend component registration
- 47 new tests (14 ACs + 33 unit tests), 103 total tests pass
- Migration 0003: plugins + plugin_migrations tables
- Coverage: 85.92% for plugin modules

app/plugins/builtins/__init__.py

@@ -0,0 +1,5 @@
+"""Built-in plugins directory.
+
+Each module in this package that exports a BasePlugin subclass will be
+discovered automatically by the plugin registry on application startup.
+"""

app/plugins/builtins/migrations/0001_bad_migration.sql

@@ -0,0 +1,7 @@
+-- Bad migration: creates table WITHOUT tenant_id (should be rejected by validator)
+CREATE TABLE IF NOT EXISTS plugin_bad_table (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    title VARCHAR(200) NOT NULL,
+    content TEXT,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT now()
+);

app/plugins/builtins/migrations/0001_test_plugin.sql

@@ -0,0 +1,10 @@
+-- Test plugin migration: creates plugin_test_data table with tenant_id
+CREATE TABLE IF NOT EXISTS plugin_test_data (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    tenant_id UUID NOT NULL,
+    title VARCHAR(200) NOT NULL,
+    content TEXT,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+CREATE INDEX IF NOT EXISTS ix_plugin_test_data_tenant ON plugin_test_data(tenant_id);

app/plugins/builtins/test_sample.py

@@ -0,0 +1,52 @@
+"""Sample test plugin for LeoCRM plugin system testing."""
+
+from __future__ import annotations
+
+from typing import Any
+
+from app.plugins.base import BasePlugin
+from app.plugins.manifest import PluginManifest
+
+
+class TestSamplePlugin(BasePlugin):
+    """A sample plugin for testing the plugin lifecycle."""
+
+    manifest = PluginManifest(
+        name="test_sample",
+        version="1.0.0",
+        display_name="Test Sample Plugin",
+        description="A sample plugin for testing install/activate/deactivate/uninstall lifecycle.",
+        dependencies=[],
+        routes=[],
+        events=["company.created", "contact.created"],
+        migrations=["0001_test_plugin.sql"],
+        permissions=[],
+    )
+
+    def __init__(self) -> None:
+        super().__init__()
+        self.install_called = False
+        self.activate_called = False
+        self.deactivate_called = False
+        self.uninstall_called = False
+        self.event_log: list[dict[str, Any]] = []
+
+    async def on_install(self, db, service_container) -> None:
+        self.install_called = True
+
+    async def on_activate(self, db, service_container, event_bus) -> None:
+        self.activate_called = True
+        await super().on_activate(db, service_container, event_bus)
+
+    async def on_deactivate(self, db, service_container, event_bus) -> None:
+        self.deactivate_called = True
+        await super().on_deactivate(db, service_container, event_bus)
+
+    async def on_uninstall(self, db, service_container) -> None:
+        self.uninstall_called = True
+
+    async def on_company_created(self, payload: dict[str, Any]) -> None:
+        self.event_log.append({"event": "company.created", "payload": payload})
+
+    async def on_contact_created(self, payload: dict[str, Any]) -> None:
+        self.event_log.append({"event": "contact.created", "payload": payload})