docs(governance): add inactivity policy for TeachLink Web (closes #1485)

[danielchukuma-dev]

Summary

Closes #1485

This PR adds the missing Governance/policies/INACTIVITY.md document and its companion regression test file Governance/policies/INACTIVITY.test.ts.

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Changes

Governance/policies/INACTIVITY.md

A new governance policy document that covers all four items required by the issue:

1. Inactivity thresholds per role

   • Contributor: 6 months of no qualifying contribution
   • Reviewer: 3 months of no completed review or comment
   • Maintainer: 2 months of no merge, review, or governance participation
   • Working-group lead / domain steward: 2 months (same as Maintainer)

2. Notification process

   • First notice 14 days before the threshold is reached
   • Second notice on the day the threshold is reached
   • 7-day response window (qualifying action, short extension, or voluntary step-down)
   • Status change recorded on a public tracking issue

3. Consequences (proportional to access, applied only after notification)

   • Contributor: status note only, no access change
   • Reviewer: removed from CODEOWNERS and review rotation
   • Maintainer: removed from team and elevated permissions
   • Working-group lead: removed from lead position; caretaker state if no co-lead

4. Reinstatement path

   • Contributor: automatic on next merged PR
   • Reviewer: two completed reviews + one Maintainer approval
   • Maintainer: four reviews/PRs in 60 days + two Maintainer approvals
   • Working-group lead: follows initial appointment process

Governance/policies/INACTIVITY.test.ts

Regression tests (vitest) that pin every concrete guarantee in the policy document to CI:

• Document structure (title, section order, no placeholders, line width ≤ 82)
• All four per-role thresholds
• All four notification steps
• Consequences for each role (including auditable tracking, caretaker state)
• Reinstatement path for each role
• Consistency with the Governance folder (referenced files exist)

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Acceptance criteria

• Governance requirement implemented — INACTIVITY.md created with all required sections
• Scope limited to two files — only INACTIVITY.md and INACTIVITY.test.ts added
• No changes outside Governance/ folder
• No regression in existing functionality
• Tests added and pass against the new document
• Change is documented in the commit message and PR description

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