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/api/v1/pdf.py

@@ -10,11 +10,23 @@ from app.api.deps import get_current_user
 from app.database import get_db
 from app.models.user import User
 from app.schemas.pdf import GeneratePdfRequest, PdfListResponse, PdfResponse
-from app.services import pdf_service
+from app.schemas.pdf_template import PdfTemplateSummaryListResponse, PdfTemplateSummaryResponse
+from app.services import pdf_service, pdf_template_service
 
 router = APIRouter(prefix="/pdf", tags=["pdf"])
 
 
+@router.get("/templates", response_model=PdfTemplateSummaryListResponse)
+async def list_available_templates(
+    _user: Annotated[User, Depends(get_current_user)],
+    db: Annotated[AsyncSession, Depends(get_db)],
+):
+    templates = await pdf_template_service.list_templates(db, active_only=True)
+    return PdfTemplateSummaryListResponse(
+        templates=[PdfTemplateSummaryResponse.model_validate(t) for t in templates]
+    )
+
+
 @router.post("/compile", response_model=PdfResponse, status_code=status.HTTP_201_CREATED)
 async def compile_pdf(
     data: GeneratePdfRequest,
@@ -22,7 +34,7 @@ async def compile_pdf(
     db: Annotated[AsyncSession, Depends(get_db)],
 ):
     pdf = await pdf_service.generate_pdf_report(
-        db, user.id, data.title, data.document_ids or None, data.chat_id,
+        db, user.id, data.title, data.document_ids or None, data.chat_id, data.template_id,
     )
     return PdfResponse.model_validate(pdf)