Build optimization: pre-built PM3 binaries, ARM64 CI, base image caching

Replace PM3 compile-from-source in pi-gen with pre-built tarball extraction
(saves 43-58 min). Merge stagePM3 into stageDangerousPi as 02-pm3-install
substage, renumber all subsequent substages. Switch CI PM3 build to native
ARM64 runner (ubuntu-24.04-arm64) eliminating QEMU overhead. Add weekly
base-image workflow for pre-baking stages 0-2. Support PM3_TARBALL,
BASE_IMAGE, and APT_PROXY env vars in build-image.sh.

Also includes prior Phase 5 work: theme system, design system integration,
component update system, OS updates, CI build pipeline, and test results.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/backend/managers/plugin_manager.py

@@ -8,6 +8,7 @@ import asyncio
 import importlib.util
 import inspect
 import json
+import re
 import time
 from dataclasses import dataclass, asdict, field
 from datetime import datetime, timezone
@@ -16,6 +17,8 @@ from pathlib import Path
 from typing import Optional, Dict, Any, List, Callable, Set
 import sys
 
+import aiohttp
+
 from .. import config
 
 
@@ -400,6 +403,18 @@ class PluginBase:
         )
 
 
+@dataclass
+class PluginUpdateInfo:
+    """Information about an available plugin update."""
+    plugin_id: str
+    current_version: str
+    available_version: str
+    changelog: str = ""
+    download_url: str = ""
+    download_size: Optional[int] = None
+    source_repo: str = ""
+
+
 class PluginManager:
     """Manages plugin loading, enabling, lifecycle, and header widgets."""
 
@@ -790,6 +805,121 @@ class PluginManager:
             del self._header_widgets[widget_id]
             print(f"Expired widget removed: {widget_id}")
 
+    # -------------------------------------------------------------------------
+    # Plugin Update Checking
+    # -------------------------------------------------------------------------
+
+    @staticmethod
+    def _extract_github_repo(homepage: Optional[str]) -> Optional[str]:
+        """Extract 'owner/repo' from a GitHub URL.
+
+        Args:
+            homepage: Plugin homepage URL
+
+        Returns:
+            'owner/repo' string or None
+        """
+        if not homepage:
+            return None
+        m = re.match(r"https?://github\.com/([^/]+/[^/]+?)(?:\.git)?/?$", homepage)
+        return m.group(1) if m else None
+
+    async def check_plugin_updates(self) -> List[PluginUpdateInfo]:
+        """Check all installed plugins for available updates.
+
+        Queries each plugin's GitHub repo (derived from homepage) for
+        newer releases. Skips plugins without a GitHub homepage.
+
+        Returns:
+            List of PluginUpdateInfo for plugins with updates available
+        """
+        updates: List[PluginUpdateInfo] = []
+
+        plugins_to_check = []
+        for plugin_id, info in self._plugins.items():
+            repo = self._extract_github_repo(info.metadata.homepage)
+            if repo:
+                plugins_to_check.append((plugin_id, info, repo))
+
+        if not plugins_to_check:
+            return updates
+
+        async with aiohttp.ClientSession() as session:
+            for plugin_id, info, repo in plugins_to_check:
+                try:
+                    update = await self._check_single_plugin_update(
+                        session, plugin_id, info, repo
+                    )
+                    if update:
+                        updates.append(update)
+                except Exception as e:
+                    print(f"Error checking updates for plugin {plugin_id}: {e}")
+
+        return updates
+
+    async def _check_single_plugin_update(
+        self,
+        session: aiohttp.ClientSession,
+        plugin_id: str,
+        info: PluginInfo,
+        repo: str,
+    ) -> Optional[PluginUpdateInfo]:
+        """Check a single plugin for available update.
+
+        Args:
+            session: aiohttp session
+            plugin_id: Plugin identifier
+            info: Current plugin info
+            repo: GitHub 'owner/repo' string
+
+        Returns:
+            PluginUpdateInfo if update available, None otherwise
+        """
+        url = f"https://api.github.com/repos/{repo}/releases/latest"
+        async with session.get(url) as resp:
+            if resp.status != 200:
+                return None
+            data = await resp.json()
+
+        latest_tag = data.get("tag_name", "").lstrip("v")
+        current_ver = info.metadata.version
+
+        if not self._is_newer_plugin_version(latest_tag, current_ver):
+            return None
+
+        # Find a suitable download asset
+        download_url = ""
+        download_size = None
+        for asset in data.get("assets", []):
+            if asset["name"].endswith((".tar.gz", ".zip")):
+                download_url = asset["browser_download_url"]
+                download_size = asset.get("size")
+                break
+
+        # Fall back to source tarball
+        if not download_url:
+            download_url = data.get("tarball_url", "")
+
+        return PluginUpdateInfo(
+            plugin_id=plugin_id,
+            current_version=current_ver,
+            available_version=latest_tag,
+            changelog=data.get("body", ""),
+            download_url=download_url,
+            download_size=download_size,
+            source_repo=repo,
+        )
+
+    @staticmethod
+    def _is_newer_plugin_version(latest: str, current: str) -> bool:
+        """Compare two version strings, returning True if latest > current."""
+        def parse(v: str) -> tuple:
+            return tuple(int(x) for x in re.split(r'[-+]', v)[0].split('.'))
+        try:
+            return parse(latest) > parse(current)
+        except (ValueError, AttributeError):
+            return latest != current
+
 
 # Global plugin manager instance
 _plugin_manager: Optional[PluginManager] = None