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/schemas/pdf_template.py

@@ -0,0 +1,59 @@
+import uuid
+from datetime import datetime
+
+from pydantic import BaseModel, Field
+
+
+class CreatePdfTemplateRequest(BaseModel):
+    name: str = Field(min_length=1, max_length=100)
+    locale: str = Field(default="en", min_length=2, max_length=10)
+    description: str | None = None
+    html_content: str = Field(min_length=1)
+
+
+class UpdatePdfTemplateRequest(BaseModel):
+    name: str | None = Field(default=None, min_length=1, max_length=100)
+    locale: str | None = Field(default=None, min_length=2, max_length=10)
+    description: str | None = None
+    html_content: str | None = Field(default=None, min_length=1)
+    is_active: bool | None = None
+
+
+class PdfTemplateResponse(BaseModel):
+    id: uuid.UUID
+    name: str
+    locale: str
+    description: str | None
+    html_content: str
+    is_default: bool
+    is_active: bool
+    created_at: datetime
+
+    model_config = {"from_attributes": True}
+
+
+class PdfTemplateListResponse(BaseModel):
+    templates: list[PdfTemplateResponse]
+
+
+class PdfTemplateSummaryResponse(BaseModel):
+    """Lightweight response for user-facing template list (no html_content)."""
+    id: uuid.UUID
+    name: str
+    locale: str
+    description: str | None
+    is_default: bool
+
+    model_config = {"from_attributes": True}
+
+
+class PdfTemplateSummaryListResponse(BaseModel):
+    templates: list[PdfTemplateSummaryResponse]
+
+
+class PreviewRequest(BaseModel):
+    html_content: str = Field(min_length=1)
+
+
+class PreviewResponse(BaseModel):
+    html: str