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/plugins/supra_theme/main.py

@@ -0,0 +1,68 @@
+"""VivoKey Supra Theme plugin for Dangerous Pi.
+
+Registers the Supra theme (Material Design 3 with VivoKey blue, rounded
+corners, elevation shadows) via the theme_register hook so it appears in
+Settings > Appearance when this plugin is enabled.
+"""
+import shutil
+import sys
+from pathlib import Path
+
+_plugin_manager_module = (
+    sys.modules.get('app.backend.managers.plugin_manager') or
+    sys.modules.get('backend.managers.plugin_manager')
+)
+if _plugin_manager_module:
+    PluginBase = _plugin_manager_module.PluginBase
+    PluginMetadata = _plugin_manager_module.PluginMetadata
+else:
+    from pathlib import Path as _P
+    app_path = _P(__file__).parent.parent.parent
+    if str(app_path) not in sys.path:
+        sys.path.insert(0, str(app_path))
+    from backend.managers.plugin_manager import PluginBase, PluginMetadata
+
+# Paths
+_PLUGIN_DIR = Path(__file__).parent
+_STATIC_CSS = _PLUGIN_DIR / "static" / "tokens.css"
+
+# Where the frontend serves themes from
+_THEMES_DIR = _PLUGIN_DIR.parent.parent / "frontend" / "themes" / "supra"
+
+
+class SupraThemePlugin(PluginBase):
+    """Provides the VivoKey Supra theme to Dangerous Pi."""
+
+    async def on_load(self):
+        pass
+
+    async def on_enable(self):
+        # Copy CSS to the themes directory so it's served by the /themes mount
+        _THEMES_DIR.mkdir(parents=True, exist_ok=True)
+        shutil.copy2(_STATIC_CSS, _THEMES_DIR / "tokens.css")
+
+        # Register the theme via the theme_register hook.
+        # MUST be synchronous — the theme scanner skips async callbacks.
+        def supra_theme_register():
+            return {
+                "id": "supra",
+                "name": "VivoKey Supra",
+                "description": "Material Design 3 with VivoKey blue, rounded corners, elevation shadows",
+                "supportsModes": ["dark", "light", "auto"],
+                "defaultMode": "dark",
+                "author": "Dangerous Things",
+                "css_url": "/themes/supra/tokens.css",
+            }
+
+        self.register_hook("theme_register", supra_theme_register)
+
+    async def on_disable(self):
+        # Clean up the copied theme files
+        if _THEMES_DIR.exists():
+            shutil.rmtree(_THEMES_DIR, ignore_errors=True)
+
+    async def on_unload(self):
+        pass
+
+    def get_metadata(self) -> PluginMetadata:
+        return self.metadata