Adds a new `/core:release` command to streamline the release process for modules.
This command automates the following workflow:
- Bumps the version in `package.json` (and `gemini-extension.json` if it exists).
- Generates a `CHANGELOG.md` entry from conventional commit messages.
- Commits the changes with a `chore(release): vX.Y.Z` message.
- Creates and pushes a new git tag to trigger the CI release.
A `--preview` flag is included to allow for a dry run of the release process without making any changes.
