Add Lucide icons, web server, and settings page cleanup

- Replace emoji icons with Lucide SVG icons (moon, sun, settings, x, upload, rotate-ccw, trash-2, save)
- Add Node.js dev server on port 3010 (server.js + npm run serve)
- Redesign settings modal: tabbed layout, styled form fields, Save/Cancel footer
- Fix dark mode: btn-danger hover now uses rgba instead of hardcoded light pink
- Fix stale pendingBranding: history item click now calls revertAndClose()
- Collapse branding header when no name/logo is set
- Move density row inline style to .density-info CSS class
- Normalise all innerText to textContent

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

package.json

@@ -5,7 +5,8 @@
   "main": "main.js",
   "scripts": {
     "start": "electron .",
-    "build": "electron-builder --win"
+    "build": "electron-builder --win",
+    "serve": "node server.js"
   },
   "author": "",
   "license": "ISC",