Release v0.21.0: UX-polish wave (#31 foundation + #24 + #25 + #32)

Token foundation + App.css sweep, header Philosophy rename, inbox
inline-SVG icon + light UX pass, session/transcript page collapse +
metadata header. Pure frontend; 332 backend tests green; build clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/package.json

@@ -1,7 +1,7 @@
 {
   "name": "rfc-app-frontend",
   "private": true,
-  "version": "0.20.0",
+  "version": "0.21.0",
   "type": "module",
   "scripts": {
     "dev": "vite",