chore(release): prepare v0.13.0-beta (#489)

- Bump version 0.12.0-beta -> 0.13.0-beta (src/vocalinux/version.py)
- README: refresh "What's New" for v0.13.0-beta and bump comparison table
- docs/UPDATE.md: add v0.13.0-beta section and bump checkout example
- SECURITY.md: mark 0.13.x supported, 0.12.x unsupported
- docs/RELEASE_PROCESS.md: add v0.13.0-beta to version history
- web: bump package.json / package-lock.json / page.tsx schema + badge
- web changelog: add v0.13.0-beta entry and refresh dateModified

web/package.json

@@ -1,6 +1,6 @@
 {
   "name": "vocalinux-website",
-  "version": "0.12.0",
+  "version": "0.13.0",
   "private": true,
   "type": "module",
   "scripts": {