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>

CLAUDE.md

@@ -45,3 +45,20 @@ The README is the primary user-facing documentation and must accurately reflect
 1. Kill existing process on port 5173
 2. Start: `cd frontend && npx vite dev --port 5173 --host &`
 3. Verify: `curl -s -o /dev/null -w "%{http_code}" http://localhost:5173/`
+
+## Frontend Architecture Notes
+
+- **i18n**: Uses `$state` rune in `.svelte.ts` file (`lib/i18n/index.svelte.ts` or `index.ts` with auto-detect). Locale auto-detects from localStorage at module load time. `t()` is reactive via `$state`. `setLocale()` updates immediately without page reload.
+- **Svelte 5 runes**: `$state` only works in `.svelte` and `.svelte.ts` files. Regular `.ts` files cannot use runes -- use plain variables instead.
+- **Static adapter**: Frontend uses `@sveltejs/adapter-static` with SPA fallback. API calls proxied via Vite dev server config.
+- **Auth flow**: After login/setup, use `window.location.href = '/'` (hard redirect), NOT `goto('/')` (races with layout auth check).
+- **Tailwind CSS v4**: Uses `@theme` directive in `app.css` for CSS variables. Grid/flex classes work but `fixed`/`absolute` positioning requires inline styles in overlay components.
+
+## Backend Architecture Notes
+
+- **SQLAlchemy async + aiohttp**: Cannot nest `async with aiohttp.ClientSession()` inside a route that has an active SQLAlchemy async session -- greenlet context breaks. Eagerly load all DB data before entering aiohttp context, or use `check_tracker_with_session()` pattern.
+- **Jinja2 SandboxedEnvironment**: All template rendering MUST use `from jinja2.sandbox import SandboxedEnvironment` (not `jinja2.sandbox.SandboxedEnvironment` -- dotted access doesn't work).
+- **System-owned entities**: `user_id=0` means system-owned (e.g. default templates). Access checks must allow `user_id == 0` in `_get()` helpers.
+- **Default templates**: Stored as `.jinja2` files in `packages/server/src/immich_watcher_server/templates/{en,ru}/`. Loaded by `load_default_templates(locale)` and seeded to DB on first startup if no templates exist.
+- **FastAPI route ordering**: Static path routes (e.g. `/variables`) MUST be registered BEFORE parameterized routes (e.g. `/{config_id}`) to avoid path conflicts.
+- **`__pycache__`**: Add to `.gitignore`. Never commit.