feat(auth): add city-core suite sessions

[scottconverse]

Run: 2026-05-28-city-core-real-non-technical-release

Scope:

• Adds CivicCore suite-session token issuance, validation, revocation, and bearer auth contracts.
• Updates CI workflow contract test to accept the logged release-verification invocation.

Local verification from C:/Users/scott/OneDrive/Desktop/Claude/civiccore:

• bash scripts/verify-release.sh -> VERIFY-RELEASE: PASSED
• python -m pytest tests/test_github_workflows.py -q -> passed

Notes:

• Conventional Commits + DCO are present on branch commits.
• No protected branch changes, force-pushes, admin merges, tags, or release artifacts.