feat: add update-available notification system

- Abstract ReleaseProvider protocol for platform-agnostic version checking
- GiteaReleaseProvider implementation using stdlib urllib
- UpdateChecker service with periodic background checks and WS broadcast
- Persistent dismissible banner in Web UI when a new version is detected
- Health endpoint now returns cached update info
- Configurable via update_check_enabled and update_check_interval settings
- i18n support (EN/RU)

media_server/services/update_checker.py

@@ -0,0 +1,120 @@
+"""Provider-agnostic update checker service."""
+
+import asyncio
+import logging
+from typing import Any, Optional
+
+from .release_provider import ReleaseProvider
+from .websocket_manager import ws_manager
+
+logger = logging.getLogger(__name__)
+
+
+def _parse_version(version: str) -> tuple[int, ...]:
+    """Parse a version string into a comparable tuple.
+
+    Handles versions like "1.0.0", "1.2.3", ignoring non-numeric suffixes.
+    """
+    parts: list[int] = []
+    for part in version.split("."):
+        digits = ""
+        for ch in part:
+            if ch.isdigit():
+                digits += ch
+            else:
+                break
+        if digits:
+            parts.append(int(digits))
+    return tuple(parts)
+
+
+class UpdateChecker:
+    """Periodically checks for new releases using a ReleaseProvider."""
+
+    def __init__(self, provider: ReleaseProvider, current_version: str) -> None:
+        self._provider = provider
+        self._current_version = current_version
+        self._current_parsed = _parse_version(current_version)
+        self._task: Optional[asyncio.Task] = None
+        self._cached_update: Optional[dict[str, Any]] = None
+
+    @property
+    def cached_update(self) -> Optional[dict[str, Any]]:
+        """Return the cached update info, or None if up-to-date."""
+        return self._cached_update
+
+    async def check_for_update(self) -> Optional[dict[str, Any]]:
+        """Check for a newer release.
+
+        Returns:
+            Dict with current/latest/url if an update exists, None otherwise.
+        """
+        release = await self._provider.get_latest_release()
+        if release is None:
+            return None
+
+        latest_parsed = _parse_version(release.version)
+        if latest_parsed <= self._current_parsed:
+            return None
+
+        return {
+            "current": self._current_version,
+            "latest": release.version,
+            "url": release.url,
+        }
+
+    async def start(self, interval: int) -> None:
+        """Start periodic update checking.
+
+        Checks immediately on start, then every `interval` seconds.
+        """
+        if self._task is not None:
+            return
+
+        self._task = asyncio.create_task(self._check_loop(interval))
+        logger.info("Update checker started (interval: %ds)", interval)
+
+    async def stop(self) -> None:
+        """Stop periodic update checking."""
+        if self._task is not None:
+            self._task.cancel()
+            try:
+                await self._task
+            except asyncio.CancelledError:
+                pass
+            self._task = None
+            logger.info("Update checker stopped")
+
+    async def _check_loop(self, interval: int) -> None:
+        """Background loop that checks for updates periodically."""
+        # Initial check with a small delay to let the server finish starting
+        await asyncio.sleep(5)
+
+        while True:
+            try:
+                update = await self.check_for_update()
+
+                if update and update != self._cached_update:
+                    self._cached_update = update
+                    logger.info(
+                        "New version available: %s → %s (%s)",
+                        update["current"],
+                        update["latest"],
+                        update["url"],
+                    )
+                    await ws_manager.broadcast(
+                        {"type": "update_available", "data": update}
+                    )
+                elif update is None and self._cached_update is not None:
+                    # Version was updated (or release removed) — clear cache
+                    self._cached_update = None
+
+            except asyncio.CancelledError:
+                break
+            except Exception as e:
+                logger.warning("Update check failed: %s", e)
+
+            try:
+                await asyncio.sleep(interval)
+            except asyncio.CancelledError:
+                break