Update the docs for a team of four #7

Goal

The docs match a team of four: the review circle, the README team line, the counts in CONTRIBUTING and standards, and the eligibility item in the brief checklist.

Builds on

#4. Updates docs from #2 and #4. No step record is touched.

Done when

• No current doc says five people or names Manish, and the dated history stays as written
• The review circle is Divyansh → Sourav → Avi → Anay → Divyansh
• The brief checklist says only contributors are listed
• docs/changes.md has an entry for the change