chore: unify version to 9.7.0 with single source of truth

- Add VERSION file at project root as canonical version source
- Sync all version references: package.json, pyproject.toml, config.py,
  Chart.yaml, docs/CONFIGURATION.md (all were out of sync: 9.0.1, v9.6, 0.1.0)
- Replace hardcoded v9.6 in SettingsPage and About page with dynamic
  APP_VERSION import from @/lib/version.ts
- Add Vite define for __APP_VERSION__ reading from package.json at build time
- Add TypeScript global declaration for __APP_VERSION__

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/package.json

@@ -1,7 +1,7 @@
 {
   "name": "frontend",
   "private": true,
-  "version": "9.0.1",
+  "version": "9.7.0",
   "type": "module",
   "scripts": {
     "dev": "vite",