Fix ephemeral issue search to support legacy expiration format

[Copilot]

The agentic maintenance job (agentics-maintenance.yml) runs every 2 hours to close expired issues, discussions, and PRs. Issues created with the legacy expiration format were not being detected and closed.

Root Cause

searchEntitiesWithExpiration only checked for the new format with HTML comment:

> - [x] expires <!-- gh-aw-expires: 2026-01-31T06:04:00.000Z --> on Jan 31, 2026, 6:04 AM UTC

Issues created with the legacy format were missed:

> - [x] expires  on Jan 31, 2026, 6:04 AM UTC

While extractExpirationDate (used to parse dates) supports both formats, the search filter only used EXPIRATION_PATTERN.

Changes

expired_entity_search_helpers.cjs

• Import both EXPIRATION_PATTERN and LEGACY_EXPIRATION_PATTERN
• Check for both patterns when filtering entities
• Log which format matched for debugging

expired_entity_search_helpers.test.cjs

• Add test case for legacy format detection
• Update logging assertion to handle format indicator

The search now finds both format variants, ensuring all expired ephemeral issues/discussions/PRs are closed regardless of creation date.

Original prompt

Investigate why the agentic maintenance job has not yet closed this issue which should have been expired already #12667

See ephemerals.js

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