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/schemas/admin.py

@@ -0,0 +1,40 @@
+import uuid
+from datetime import datetime
+
+from typing import Literal
+
+from pydantic import BaseModel, EmailStr, Field
+
+
+class AdminUserResponse(BaseModel):
+    id: uuid.UUID
+    email: str
+    username: str
+    full_name: str | None
+    role: str
+    is_active: bool
+    max_chats: int
+    created_at: datetime
+
+    model_config = {"from_attributes": True}
+
+
+class AdminUserCreateRequest(BaseModel):
+    email: EmailStr
+    username: str = Field(min_length=3, max_length=50, pattern=r"^[a-zA-Z0-9_-]+$")
+    password: str = Field(min_length=8, max_length=128)
+    full_name: str | None = None
+    role: Literal["user", "admin"] = "user"
+    max_chats: int = 10
+
+
+class AdminUserUpdateRequest(BaseModel):
+    role: Literal["user", "admin"] | None = None
+    is_active: bool | None = None
+    max_chats: int | None = None
+    full_name: str | None = None
+
+
+class AdminUserListResponse(BaseModel):
+    users: list[AdminUserResponse]
+    total: int