Fix UI issues: locale switching, dark theme, loading, edit support

- Fix i18n: remove $state rune (SSR incompatible in .ts files),
  use reactive localeVersion counter in layout to trigger re-render
  on locale change. Language switching now works immediately.
- Fix dark theme: add global CSS rules for input/select/textarea to
  use theme colors, override browser autofill in dark mode, set
  color-scheme for native controls (scrollbars, checkboxes)
- Collapsible sidebar: toggle button (▶/◀) with persistent state,
  icons-only mode when collapsed. Theme/language buttons moved to
  bottom above user info.
- Loading skeletons: all pages show animated pulse placeholders
  while data loads, eliminating content flicker on tab switch
- Edit support: Servers, Trackers, and Targets now have Edit buttons
  that open the form pre-filled with current values. Save calls PUT.
  Sensitive fields (API key, bot token) can be left empty to keep
  current value when editing.
- CLAUDE.md: add dev server restart rules

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

CLAUDE.md

@@ -30,3 +30,16 @@ When modifying the integration interface, you MUST update the corresponding docu
 - **services.yaml**: Keep service definitions in sync with implementation
 
 The README is the primary user-facing documentation and must accurately reflect the current state of the integration.
+
+## Development Servers
+
+**IMPORTANT**: When the user requests it OR when backend code changes are made (files in `packages/server/`), you MUST restart the standalone server:
+1. Kill the existing process on port 8420
+2. Reinstall: `cd packages/server && pip install -e .`
+3. Start: `cd <repo_root> && IMMICH_WATCHER_DATA_DIR=./test-data IMMICH_WATCHER_SECRET_KEY=test-secret-key-minimum-32chars nohup python -m uvicorn immich_watcher_server.main:app --host 0.0.0.0 --port 8420 > /dev/null 2>&1 &`
+4. Verify: `curl -s http://localhost:8420/api/health`
+
+**IMPORTANT**: When the user requests it, restart the frontend dev server:
+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/`