Set up trusted publishing Fixes

[dhuebner]

This pull request overhauls the release process documentation and automates publishing for the npm packages. It introduces new GitHub Actions workflows for both "next" and "latest" releases, replaces the old releasing.md with a much more detailed and actionable RELEASING.md, and updates references throughout the documentation to match the new file name. These changes make the release process more robust, transparent, and secure by leveraging npm's staged publishing and trusted publishing via OIDC.

Release process automation and documentation:

• Added .github/workflows/publish-next.yml to automate staging "next" snapshot releases of vscode-messenger-common, vscode-messenger, and vscode-messenger-webview to npm under the next tag, using npm trusted publishing and staged publishing for added security.
• Added .github/workflows/publish.yml to automate staging production ("latest") releases of the same packages, triggered by semver tags or manually, also using trusted and staged publishing.
• Replaced the old releasing.md with a new, comprehensive RELEASING.md that provides step-by-step instructions for both manual and CI-based releases, including how to review, approve, or reject staged npm packages, and updated guidance for the devtools extension. [1] [2]

NOTE: vs-code extension publishing will be handled separately in follow-up PR when a new extension release is required.

Documentation consistency:

• Updated all references in AGENTS.md from releasing.md to RELEASING.md to match the new file name and ensure consistency across documentation. [1] [2]