chore: release v0.12.1

Bump root/backend/frontend to 0.12.1 and move the CHANGELOG notes under a dated
0.12.1 heading (centered wallet-sync stepper, timeline record history, and the
landing-page globe deferral). Adds the radix-ui dependency pulled in by the
Origin UI stepper/timeline primitives.

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "temetro",
-  "version": "0.12.0",
+  "version": "0.12.1",
   "private": true,
   "devDependencies": {
     "shadcn": "^4.11.0"