refactor: restructure project into muxplex/ subdir with brand integration

- Move coordinator/, frontend/, Caddyfile, pyproject.toml, requirements.txt,
  docs/ into muxplex/ subdir in prep for packaging/sharing
- Add brand assets to frontend/: favicon.ico, pwa-192/512.png,
  apple-touch-icon.png, wordmark-on-dark.svg
- Update app: title → muxplex, header → wordmark SVG, brand color tokens
  in style.css, manifest.json updated with muxplex name and brand icons
- Add design system: assets/branding/tokens.css (101 CSS custom properties),
  tokens.json (127 tokens), DESIGN-SYSTEM.md (856-line spec)
- Add assets/branding/: SVG sources, rendered PNGs (icons, favicons, PWA, OG)
- Add scripts/render-brand-assets.py for reproducible PNG generation
- Add muxplex/README.md

frontend/manifest.json

@@ -0,0 +1,14 @@
+{
+  "name": "muxplex",
+  "short_name": "muxplex",
+  "description": "Browser-based tmux session dashboard",
+  "start_url": "/",
+  "display": "standalone",
+  "orientation": "any",
+  "background_color": "#0D1117",
+  "theme_color": "#0D1117",
+  "icons": [
+    {"src": "/pwa-192.png", "sizes": "192x192", "type": "image/png", "purpose": "any"},
+    {"src": "/pwa-512.png", "sizes": "512x512", "type": "image/png", "purpose": "any maskable"}
+  ]
+}