feat(themes): Terrakotta replaces High Contrast; equal header buttons on phones

chore(release): v0.12.0

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "mindsift-frontend",
-  "version": "0.11.1",
+  "version": "0.12.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "mindsift-frontend",
-      "version": "0.11.1",
+      "version": "0.12.0",
       "license": "Unlicense",
       "dependencies": {
         "@fontsource-variable/inter": "5.3.0",