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/frontend/package.json

@@ -13,6 +13,7 @@
     "@remix-run/node": "^2.14.0",
     "@remix-run/react": "^2.14.0",
     "@remix-run/serve": "^2.14.0",
+    "@dangerousthings/web": "file:../../../dt-design-system/packages/web",
     "html5-qrcode": "^2.3.8",
     "react": "^18.3.1",
     "react-dom": "^18.3.1"