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/templates/en/album_deleted.jinja2

@@ -0,0 +1 @@
+🗑️ Album "{{ album_name }}" was deleted.

packages/server/src/immich_watcher_server/templates/en/album_renamed.jinja2

@@ -0,0 +1 @@
+✏️ Album "{{ old_name }}" renamed to "{{ new_name }}".

packages/server/src/immich_watcher_server/templates/en/assets_added.jinja2

@@ -0,0 +1,12 @@
+📷 {{ added_count }} new photo(s) added to album "{{ album_name }}".
+{%- if people %}
+👤 {{ people | join(", ") }}
+{%- endif %}
+{%- if added_assets %}
+{%- for asset in added_assets %}
+  • {%- if asset.type == "VIDEO" %} 🎬{% else %} 🖼️{% endif %} {{ asset.filename }}
+    {%- if asset.city %} 📍 {{ asset.city }}{% if asset.country %}, {{ asset.country }}{% endif %}{% endif %}
+    {%- if asset.is_favorite %} ❤️{% endif %}
+{%- endfor %}
+{%- endif %}
+{{ video_warning }}

packages/server/src/immich_watcher_server/templates/en/assets_removed.jinja2

@@ -0,0 +1 @@
+🗑️ {{ removed_count }} photo(s) removed from album "{{ album_name }}".

packages/server/src/immich_watcher_server/templates/en/memory_mode.jinja2

@@ -0,0 +1,4 @@
+📅 On this day:
+{%- for asset in assets %}
+  • {%- if asset.type == "VIDEO" %} 🎬{% else %} 🖼️{% endif %} {{ asset.filename }} ({{ asset.created_at[:4] }})
+{%- endfor %}

packages/server/src/immich_watcher_server/templates/en/periodic_summary.jinja2

@@ -0,0 +1,5 @@
+📋 Tracked Albums Summary ({{ albums | length }} albums):
+{%- for album in albums %}
+  • {{ album.name }}: {{ album.asset_count }} assets
+    {%- if album.url %} — {{ album.url }}{% endif %}
+{%- endfor %}

packages/server/src/immich_watcher_server/templates/en/scheduled_assets.jinja2

@@ -0,0 +1,4 @@
+📸 Photos from "{{ album_name }}":
+{%- for asset in assets %}
+  • {%- if asset.type == "VIDEO" %} 🎬{% else %} 🖼️{% endif %} {{ asset.filename }}
+{%- endfor %}