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

extension/shared/README.md

@@ -1,14 +0,0 @@
-# ⚠️ READ BEFORE EDITING
-
-This directory is a **MIRROR** of the root `/shared` folder.
-
-**DO NOT edit these files directly.** Any changes made here will be overwritten the next time the synchronization script is run.
-
-### Proper Workflow:
-1.  **Edit** the source files in the root `[repo_root]/shared/` directory.
-2.  **Run** the synchronization script:
-    -   **Windows**: `[repo_root]\scripts\sync-constants.bat`
-    -   **Linux/macOS**: `[repo_root]/scripts/sync-constants.sh`
-3.  **Verify** that the changes have propagated to this folder.
-
-Failure to follow this protocol will result in out-of-sync components and broken protocol logic.