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.

.gitignore

@@ -1,2 +0,0 @@
-/gh-commit
-dist/