feat: implement audit trail module

- Backend (FastAPI):
  - AuditLog and AuditAlert models with Alembic migration
  - AuditService with SHA-256 checksum for log integrity
  - AuditMiddleware for request metadata extraction (IP, user_agent)
  - Integrated audit logging into Task, Project, Blocker APIs
  - Query API with filtering, pagination, CSV export
  - Integrity verification endpoint
  - Sensitive operation alerts with acknowledgement

- Frontend (React + Vite):
  - Admin AuditPage with filters and export
  - ResourceHistory component for change tracking
  - Audit service for API calls

- Testing:
  - 15 tests covering service and API endpoints

- OpenSpec:
  - add-audit-trail change archived

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/schemas/__init__.py

@@ -20,6 +20,10 @@ from app.schemas.notification import (
 from app.schemas.blocker import (
     BlockerCreate, BlockerResolve, BlockerResponse, BlockerListResponse
 )
+from app.schemas.audit import (
+    AuditLogResponse, AuditLogListResponse, AuditAlertResponse, AuditAlertListResponse,
+    IntegrityCheckRequest, IntegrityCheckResponse
+)
 
 __all__ = [
     "LoginRequest",
@@ -64,4 +68,10 @@ __all__ = [
     "BlockerResolve",
     "BlockerResponse",
     "BlockerListResponse",
+    "AuditLogResponse",
+    "AuditLogListResponse",
+    "AuditAlertResponse",
+    "AuditAlertListResponse",
+    "IntegrityCheckRequest",
+    "IntegrityCheckResponse",
 ]