Security fixes: P0-P2 complete (22 fixes)

P0 (7): Auth-bypass removed, migrations fixed, plugin-upload disabled, RLS FORCE+WITH CHECK, plugin double-registration fixed, persistent volume, domain removed
P1 (11): User/tenant model, Redis centralized, worker separated, transactional outbox, XSS fixed, DMS chunked streaming, permissions unified, password reset, metrics secured, config/docs fixed, cross-tenant FK
P2 (4): Contact model normalized, cross-imports reduced 94%, commands+state machines for contacts/dms/mail/calendar, SPA path-traversal

8 new migrations, 99 unit tests, 13 commands, 8 contracts, 72 files changed

app/plugins/builtins/ai_assistant/contracts.py

@@ -0,0 +1,60 @@
+"""Public contract for the ai_assistant plugin.
+
+Exposes only the symbols that other builtins plugins need:
+- Tool registry (register, unregister, list tools)
+- get_default_provider (for LLM provider lookup)
+
+Importers should use::
+
+    from app.plugins.builtins.contracts import get_contract
+    ai = get_contract("ai_assistant")
+    if ai:
+        registry = ai.get_tool_registry()
+        registry.register("my_tool", ...)
+
+instead of importing from internal modules directly.
+"""
+
+from __future__ import annotations
+
+from app.plugins.builtins.ai_assistant.services import get_default_provider
+from app.plugins.builtins.ai_assistant.tool_registry import (
+    AITool,
+    ToolRegistry,
+    get_tool_registry,
+)
+from app.plugins.builtins.contracts import get_contract_registry
+
+
+class AIAssistantContract:
+    """Public API surface for the ai_assistant plugin.
+
+    Exposes the tool registry and the default-provider lookup so that
+    other plugins can register AI tools and obtain the tenant's default
+    LLM provider without importing internal modules.
+    """
+
+    contract_name = "ai_assistant"
+
+    # ─── tool registry ───
+    get_tool_registry = staticmethod(get_tool_registry)
+    ToolRegistry = ToolRegistry
+    AITool = AITool
+
+    # ─── provider lookup ───
+    get_default_provider = staticmethod(get_default_provider)
+
+
+# ─── self-registration ───
+
+_contract = AIAssistantContract()
+get_contract_registry().register("ai_assistant", _contract)
+
+
+__all__ = [
+    "AIAssistantContract",
+    "AITool",
+    "ToolRegistry",
+    "get_tool_registry",
+    "get_default_provider",
+]