Initialize a new Mantine minor or major release: creates a git branch, sets up the changelog MDX page, updates mdx-meta-data.ts, mdx-nav-data.ts, and versions.ts, and commits. Use when the user wants to start a new release (e.g., "new release 9.1.0", "/new-mantine-release 9.1.0", "initialize 9.2.0 release").