Phase 8: Customizable PDF Templates — locale support, admin editor, seed templates

Backend:
- PdfTemplate model with locale field + UNIQUE(name, locale) constraint
- Migration 007: pdf_templates table + template_id FK on generated_pdfs
- Template service: CRUD, Jinja2 validation, render preview with sample data
- Admin endpoints: CRUD /admin/pdf-templates + POST preview
- User endpoint: GET /pdf/templates (active templates list)
- pdf_service: resolves template from DB by ID or falls back to default
  for the appropriate locale
- AI generate_pdf tool accepts optional template_id
- Seed script + 4 HTML template files:
  - Basic Report (en/ru) — general-purpose report
  - Medical Report (en/ru) — health-focused with disclaimers

Frontend:
- Admin PDF templates page with editor, locale selector, live preview (iframe),
  template variables reference panel
- PDF page: template selector dropdown in generation form
- API clients for admin CRUD + user template listing
- Sidebar: admin templates link
- English + Russian translations

Also added Phase 9 (OAuth) and Phase 10 (Rate Limits) placeholders to GeneralPlan.

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

backend/app/services/ai_service.py

@@ -99,6 +99,7 @@ AI_TOOLS = [
             "type": "object",
             "properties": {
                 "title": {"type": "string", "description": "Title for the PDF report"},
+                "template_id": {"type": "string", "description": "Optional UUID of a specific PDF template to use"},
             },
             "required": ["title"],
         },
@@ -174,7 +175,8 @@ async def _execute_tool(
 
     elif tool_name == "generate_pdf":
         from app.services.pdf_service import generate_pdf_report
-        pdf = await generate_pdf_report(db, user_id, title=tool_input["title"])
+        tmpl_id = uuid.UUID(tool_input["template_id"]) if tool_input.get("template_id") else None
+        pdf = await generate_pdf_report(db, user_id, title=tool_input["title"], template_id=tmpl_id)
         await db.commit()
         return json.dumps({
             "status": "generated",