refactor: replace Go binary with uv-run smartcommit.py launcher

The extension is now a bash launcher that runs smartcommit.py via
uv run --script (Crush backend, DuckDB scopes). Removes the Go
implementation and the gh-extension-precompile workflow; the bundled
gh-commit.tar.gz now packages the script instead of a compiled binary.

smartcommit.py

@@ -52,7 +52,7 @@ AUTO_PUSH = os.environ.get("GH_COMMIT_PUSH", "0") == "1"
 NO_AUTO_REFRESH = os.environ.get("GH_COMMIT_NO_AUTO_REFRESH", "0") == "1"
 DEBUG = os.environ.get("GH_COMMIT_DEBUG", "0") == "1"
 
-VERSION = "2.0.0"
+VERSION = "5.0.0"
 
 
 # ── Helpers ───────────────────────────────────────────────────────────────────