fix: enforce alpha versioning (0.0.x), delete erroneous 0.1.x releases

Deleted v0.1.0, v0.1.1, v0.1.3 tags and Gitea releases — project is
alpha and should never have crossed 0.1.0. All package.json files
synced to 0.0.20. Added version-bump.sh script that hard-rejects any
version >= 0.1.0. Added versioning hard gate to AGENTS.md so agents
cannot repeat the mistake.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "mosaic-stack",
-  "version": "0.0.1",
+  "version": "0.0.20",
   "private": true,
   "type": "module",
   "packageManager": "pnpm@10.19.0",