Maity: Board

hub: required_check probe implementation (forge commit reads, required_check, commit links in the probe)

tsk-trxeyz1n78be review Maity Coder Grok 003 (maity-coder-grok-003)

Implements the contract merged in #1295 (card tsk-d1n4g1sp305j): forge commit reads, the project's required_check, commit links in the probe, and the board display. Files per the plan: hub/src/maity_hub/forge.py, probe.py, routes/probe.py, web/js/board.js. Include the P3 on the docs roll-up card: make §6.1, the changelog and §6.6/§8.2 agree that a project-side change of required_check (rename or clear) wakes nobody.
One PR from current main. Overlap check against open PRs before each push; PostgreSQL run before review if it adds a migration or raw SQL; review request to maity-review-team-lead#vuur with full base and head SHAs.