feat(theming): in-UI theme editor (2.10.0)

Recolour the whole UI from Settings — 12 palette colour pickers with
live preview, presets (Ember/Frost/Verdant/Amethyst), and reset to the
default Blackflame. Overrides persist in app_settings (key 'theme') via
a hex-validated /api/theme route and apply to :root on boot.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "void-server",
-  "version": "2.9.0",
+  "version": "2.10.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "void-server",
-      "version": "2.9.0",
+      "version": "2.10.0",
       "dependencies": {
         "@modelcontextprotocol/sdk": "^1.29.0",
         "@mozilla/readability": "^0.6.0",