feat: add auto-update system with release checking, notification UI, and install-type-aware apply

- Abstract ReleaseProvider interface (Gitea impl, swappable for GitHub/GitLab)
- Background UpdateService with periodic checks, debounce, dismissed version persistence
- Install type detection (installer/portable/docker/dev) with platform-aware asset matching
- Download with progress events, silent NSIS reinstall, portable ZIP/tarball swap scripts
- Version badge pulse animation, dismissible banner with icon buttons, Settings > Updates tab
- Single source of truth: pyproject.toml version via importlib.metadata, CI stamps tag with sed
- API: GET/POST status, check, dismiss, apply, GET/PUT settings
- i18n: en, ru, zh (27+ keys each)

contexts/auto-update-plan.md

@@ -0,0 +1,143 @@
+# Auto-Update Plan — Phase 1: Check & Notify
+
+> Created: 2026-03-25. Status: **planned, not started.**
+
+## Backend Architecture
+
+### Release Provider Abstraction
+
+```
+core/update/
+    release_provider.py   — ABC: get_releases(), get_releases_page_url()
+    gitea_provider.py     — Gitea REST API implementation
+    version_check.py      — normalize_version(), is_newer() using packaging.version
+    update_service.py     — Background asyncio task + state machine
+```
+
+**`ReleaseProvider` interface** — two methods:
+- `get_releases(limit) → list[ReleaseInfo]` — fetch releases (newest first)
+- `get_releases_page_url() → str` — link for "view on web"
+
+**`GiteaReleaseProvider`** calls `GET {base_url}/api/v1/repos/{repo}/releases`. Swapping to GitHub later means implementing the same interface against `api.github.com`.
+
+**Data models:**
+
+```python
+@dataclass(frozen=True)
+class AssetInfo:
+    name: str          # "LedGrab-v0.3.0-win-x64.zip"
+    size: int          # bytes
+    download_url: str
+
+@dataclass(frozen=True)
+class ReleaseInfo:
+    tag: str           # "v0.3.0"
+    version: str       # "0.3.0"
+    name: str          # "LedGrab v0.3.0"
+    body: str          # release notes markdown
+    prerelease: bool
+    published_at: str  # ISO 8601
+    assets: tuple[AssetInfo, ...]
+```
+
+### Version Comparison
+
+`version_check.py` — normalize Gitea tags to PEP 440:
+- `v0.3.0-alpha.1` → `0.3.0a1`
+- `v0.3.0-beta.2` → `0.3.0b2`
+- `v0.3.0-rc.3` → `0.3.0rc3`
+
+Uses `packaging.version.Version` for comparison.
+
+### Update Service
+
+Follows the **AutoBackupEngine pattern**:
+- Settings in `Database.get_setting("auto_update")`
+- asyncio.Task for periodic checks
+- 30s startup delay (avoid slowing boot)
+- 60s debounce on manual checks
+
+**State machine (Phase 1):** `IDLE → CHECKING → UPDATE_AVAILABLE`
+
+No download/apply in Phase 1 — just detection and notification.
+
+**Settings:** `enabled` (bool), `check_interval_hours` (float), `channel` ("stable" | "pre-release")
+
+**Persisted state:** `dismissed_version`, `last_check` (survives restarts)
+
+### API Endpoints
+
+| Method | Path | Purpose |
+|--------|------|---------|
+| `GET` | `/api/v1/system/update/status` | Current state + available version |
+| `POST` | `/api/v1/system/update/check` | Trigger immediate check |
+| `POST` | `/api/v1/system/update/dismiss` | Dismiss notification for current version |
+| `GET` | `/api/v1/system/update/settings` | Get settings |
+| `PUT` | `/api/v1/system/update/settings` | Update settings |
+
+### Wiring
+
+- New `get_update_service()` in `dependencies.py`
+- `UpdateService` created in `main.py` lifespan, `start()`/`stop()` alongside other engines
+- Router registered in `api/__init__.py`
+- WebSocket event: `update_available` fired via `processor_manager.fire_event()`
+
+## Frontend
+
+### Version badge highlight
+
+The existing `#server-version` pill in the header gets a CSS class `has-update` when a newer version exists — changes the background to `var(--warning-color)` with a subtle pulse, making it clickable to open the update panel in settings.
+
+### Notification popup
+
+On `server:update_available` WebSocket event (and on page load if status says `has_update` and not dismissed):
+- A **persistent dismissible banner** slides in below the header (not the ephemeral 3s toast)
+- Shows: "Version {x.y.z} is available" + [View Release Notes] + [Dismiss]
+- Dismiss calls `POST /dismiss` and hides the bar for that version
+- Stored in `localStorage` so it doesn't re-show after page refresh for dismissed versions
+
+### Settings tab: "Updates"
+
+New 5th tab in the settings modal:
+- Current version display
+- "Check for updates" button + spinner
+- Channel selector (stable / pre-release) via IconSelect
+- Auto-check toggle + interval selector
+- When update available: release name, notes preview, link to releases page
+
+### i18n keys
+
+New `update.*` keys in `en.json`, `ru.json`, `zh.json` for all labels.
+
+## Files to Create
+
+| File | Purpose |
+|------|---------|
+| `core/update/__init__.py` | Package init |
+| `core/update/release_provider.py` | Abstract provider interface + data models |
+| `core/update/gitea_provider.py` | Gitea API implementation |
+| `core/update/version_check.py` | Semver normalization + comparison |
+| `core/update/update_service.py` | Background service + state machine |
+| `api/routes/update.py` | REST endpoints |
+| `api/schemas/update.py` | Pydantic request/response models |
+
+## Files to Modify
+
+| File | Change |
+|------|--------|
+| `api/__init__.py` | Register update router |
+| `api/dependencies.py` | Add `get_update_service()` |
+| `main.py` | Create & start/stop UpdateService in lifespan |
+| `templates/modals/settings.html` | Add Updates tab |
+| `static/js/features/settings.ts` | Update check/settings UI logic |
+| `static/js/core/api.ts` | Version badge highlight on health check |
+| `static/css/layout.css` | `.has-update` styles for version badge |
+| `static/locales/en.json` | i18n keys |
+| `static/locales/ru.json` | i18n keys |
+| `static/locales/zh.json` | i18n keys |
+
+## Future Phases (not in scope)
+
+- **Phase 2**: Download & stage artifacts
+- **Phase 3**: Apply update & restart (external updater script, NSIS silent mode)
+- **Phase 4**: Checksums, "What's new" dialog, update history