feat(sdk): Multi-Projekt-Architektur — mehrere Projekte pro Tenant

Jeder Tenant kann jetzt mehrere Compliance-Projekte anlegen (z.B. verschiedene
Produkte, Tochterunternehmen). CompanyProfile ist pro Projekt kopierbar und
danach unabhaengig editierbar. Multi-Tab-Support via separater BroadcastChannel
und localStorage Keys pro Projekt.

- Migration 039: compliance_projects Tabelle, sdk_states.project_id
- Backend: FastAPI CRUD-Routes fuer Projekte mit Tenant-Isolation
- Frontend: ProjectSelector UI, SDKProvider mit projectId, URL ?project=
- State API: UPSERT auf (tenant_id, project_id) mit Abwaertskompatibilitaet
- Tests: pytest fuer Model-Validierung, Row-Konvertierung, Tenant-Isolation
- Docs: MKDocs Seite, CLAUDE.md, Backend README

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend-compliance/compliance/api/__init__.py

@@ -31,6 +31,7 @@ from .vendor_compliance_routes import router as vendor_compliance_router
 from .incident_routes import router as incident_router
 from .change_request_routes import router as change_request_router
 from .generation_routes import router as generation_router
+from .project_routes import router as project_router
 
 # Include sub-routers
 router.include_router(audit_router)
@@ -63,6 +64,7 @@ router.include_router(vendor_compliance_router)
 router.include_router(incident_router)
 router.include_router(change_request_router)
 router.include_router(generation_router)
+router.include_router(project_router)
 
 __all__ = [
     "router",
@@ -95,4 +97,5 @@ __all__ = [
     "incident_router",
     "change_request_router",
     "generation_router",
+    "project_router",
 ]