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/services/setting_service.py

@@ -0,0 +1,33 @@
+import uuid
+
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.models.setting import Setting
+
+
+async def get_setting(db: AsyncSession, key: str) -> Setting | None:
+    result = await db.execute(select(Setting).where(Setting.key == key))
+    return result.scalar_one_or_none()
+
+
+async def get_setting_value(db: AsyncSession, key: str, default=None):
+    setting = await get_setting(db, key)
+    return setting.value if setting else default
+
+
+async def get_all_settings(db: AsyncSession) -> list[Setting]:
+    result = await db.execute(select(Setting).order_by(Setting.key))
+    return list(result.scalars().all())
+
+
+async def upsert_setting(db: AsyncSession, key: str, value, admin_user_id: uuid.UUID) -> Setting:
+    setting = await get_setting(db, key)
+    if setting:
+        setting.value = value
+        setting.updated_by = admin_user_id
+    else:
+        setting = Setting(key=key, value=value, updated_by=admin_user_id)
+        db.add(setting)
+    await db.flush()
+    return setting