Phase 6: PDF & Polish — PDF generation, admin users/settings, AI tool

Backend:
- Setting + GeneratedPdf models, Alembic migration with default settings seed
- PDF generation service (WeasyPrint + Jinja2 with autoescape)
- Health report HTML template with memory entries + document excerpts
- Admin user management: list, create, update (role/max_chats/is_active)
- Admin settings: self_registration_enabled, default_max_chats
- Self-registration check wired into auth register endpoint
- default_max_chats applied to new user registrations
- AI tool: generate_pdf creates health compilation PDFs
- PDF compile/list/download API endpoints
- WeasyPrint system deps added to Dockerfile

Frontend:
- PDF reports page with generate + download
- Admin users page with create/edit/activate/deactivate
- Admin settings page with self-registration toggle + max chats
- Extended sidebar with PDF reports + admin users/settings links
- English + Russian translations for all new UI

Review fixes applied:
- Jinja2 autoescape enabled (XSS prevention in PDFs)
- db.refresh after flush (created_at populated correctly)
- storage_path removed from API response (no internal path leak)
- Role field uses Literal["user", "admin"] validation
- React hooks called before conditional returns (rules of hooks)
- default_max_chats setting now applied during registration

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/api/v1/router.py

@@ -9,6 +9,7 @@ from app.api.v1.documents import router as documents_router
 from app.api.v1.memory import router as memory_router
 from app.api.v1.notifications import router as notifications_router
 from app.api.v1.ws import router as ws_router
+from app.api.v1.pdf import router as pdf_router
 
 api_v1_router = APIRouter(prefix="/api/v1")
 
@@ -21,6 +22,7 @@ api_v1_router.include_router(documents_router)
 api_v1_router.include_router(memory_router)
 api_v1_router.include_router(notifications_router)
 api_v1_router.include_router(ws_router)
+api_v1_router.include_router(pdf_router)
 
 
 @api_v1_router.get("/health")