Fix expiration detection for quoted footers and legacy format

[Copilot]

Issue #10667 expired Jan 20 but wasn't closed by agentic-maintenance. The expiration pattern didn't match blockquote-prefixed lines (> - [x] expires...) and had no fallback for issues created before HTML comments were added.

Changes

• Updated EXPIRATION_PATTERN to require blockquote prefix: /^>\s*-\s*\[x\]\s+expires\s*<!--\s*gh-aw-expires:\s*([^>]+)\s*-->/m
• Added LEGACY_EXPIRATION_PATTERN to match old format without HTML comment: /^>\s*-\s*\[x\]\s+expires\s+on\s+(.+?)\s+UTC\s*$/m
• Updated extractExpirationDate() to try new format first, fall back to legacy format parsing human-readable dates

Example

// New format (with ISO timestamp in HTML comment)
"> - [x] expires <!-- gh-aw-expires: 2026-01-20T09:20:00.000Z --> on Jan 20, 2026, 9:20 AM UTC"
// ✓ Matched by EXPIRATION_PATTERN, extracts ISO date

// Legacy format (issue #10667)
"> - [x] expires  on Jan 20, 2026, 9:20 AM UTC"
// ✓ Matched by LEGACY_EXPIRATION_PATTERN, parses human-readable date

Both formats now work. Next maintenance run will detect and close #10667.

Original prompt

review agentic-maintenance.yml code that expires issues. This issue should have expired and it should have been closed.

#10667

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