[imorland]

Fixes: follow-up to #5111, #4623 and #5354

Changes proposed in this pull request:

• Adds support.docs to flarum/ai, flarum/mcp and flarum/oauth-provider, pointing at https://docs.flarum.org/extensions/<name>, as the other bundled extensions do.
• flarum/mcp requires flarum/oauth-provider: ^2.1 instead of *@dev, like akismet's flarum/approval: ^2.1. In the monorepo, replace provides it at self.version; the split package resolves once 2.1.0 is tagged.

Reviewers should focus on:

• The oauth-provider page is in docs: document the OAuth Provider extension docs#697. The ai and mcp pages don't exist yet, so those two links lead nowhere until they are written.

Necessity

• Has the problem that is being solved here been clearly explained?
• If applicable, have various options for solving this problem been considered? (Not applicable.)
• For core PRs, does this need to be in core, or could it be in an extension?
• Are we willing to maintain this for years / potentially forever?

Confirmed

• Frontend changes: tested on a local Flarum installation. (No frontend changes.)
• Frontend changes: tests are green (run yarn test in js/). (No frontend changes.)
• Frontend changes: tests have been added, or are not appropriate here. (No frontend changes.)
• Backend changes: tests are green (run composer test). (Only composer metadata changes.)
• Backend changes: tests have been added, or are not appropriate here. (Only composer metadata changes.)
• Where applicable, changes are suitable for all supported database drivers (MySQL, MariaDB, PostgreSQL, SQLite). (No database changes.)
• Core developer confirmed locally this works as intended.
• The description above is written by me and describes what this pull request actually does.