Move default templates to .jinja2 files + add live preview + update CLAUDE.md

Templates:
- Default EN/RU templates moved from inline Python strings to
  14 .jinja2 files in templates/{en,ru}/ directory
- Properly formatted with readable indentation and Jinja2
  whitespace control ({%- -%})
- load_default_templates(locale) loads from files on first access
- Seed function uses file loader instead of inline dicts

Preview:
- New POST /api/template-configs/preview-raw endpoint: renders
  arbitrary Jinja2 text with sample data (for live editing preview)
- Route ordering fixed: /variables before /{config_id}

CLAUDE.md:
- Added Frontend Architecture Notes (i18n, Svelte 5 runes, auth
  flow, Tailwind v4 quirks)
- Added Backend Architecture Notes (SQLAlchemy+aiohttp greenlet
  issue, SandboxedEnvironment import, system-owned entities,
  FastAPI route ordering, __pycache__)

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

packages/server/src/immich_watcher_server/api/template_configs.py

@@ -157,6 +157,25 @@ async def preview_config(
         raise HTTPException(status_code=400, detail=f"Template error: {e}")
 
 
+class PreviewRequest(BaseModel):
+    template: str
+
+
+@router.post("/preview-raw")
+async def preview_raw(
+    body: PreviewRequest,
+    user: User = Depends(get_current_user),
+):
+    """Render arbitrary Jinja2 template text with sample data. For live preview while editing."""
+    try:
+        env = SandboxedEnvironment(autoescape=False)
+        tmpl = env.from_string(body.template)
+        rendered = tmpl.render(**_SAMPLE_CONTEXT)
+        return {"rendered": rendered}
+    except Exception as e:
+        return {"rendered": None, "error": str(e)}
+
+
 def _response(c: TemplateConfig) -> dict:
     return {k: getattr(c, k) for k in TemplateConfig.model_fields if k != "user_id"} | {
         "created_at": c.created_at.isoformat()