ci: auto-inject version from git tag + unify shared/ mirroring

- CI release workflow now extracts version from tag (v1.4.0 → 1.4.0)
  and injects it into manifest.base.json, shared/constants.js, and
  package.json before building — the tag is the single source of truth
- Build script now copies README.md alongside constants.js and
  blacklist.js from /shared → /extension/shared/ (full mirror)
- .gitignore updated: extension/shared/ is fully generated by build
- AI_INIT.md: simplified release workflow, fixed Chrome-only reference

.gitignore

@@ -38,8 +38,7 @@ coverage/
 # KoalaSync Specific
 # We ignore the synced files in the extension folder to ensure 
 # the root 'shared/' remains the Single Source of Truth.
-extension/shared/*
-!extension/shared/README.md
+extension/shared/
 
 # Temporary scratch files
 scratch/