M5: Retention Cleanup + Tests + Documentation

[Jasonnnz]

Adds qaRecording config section, periodic cleanup worker for expired file-backed recordings, ARCHITECTURE.md documentation for QA video data flow, and cleanup tests. Part of #6899.

Changes

Config (qaRecording section)

• defaultRetentionDays (default: 7) — how long recordings are kept
• cleanupIntervalMs (default: 6 hours) — how often the cleanup worker runs

Cleanup worker (recording-cleanup.ts)

• Runs one pass on daemon startup to catch recordings that expired while offline
• Runs periodically on the configured interval
• For each expired file-backed attachment: deletes file from disk, removes DB row, logs summary
• Wired into lifecycle.ts init/shutdown

Tests (recording-cleanup.test.ts)

• Expired file-backed attachments are cleaned up (files deleted, DB rows removed)
• Non-expired attachments are NOT cleaned up
• Inline base64 attachments are never touched by cleanup
• Missing files handled gracefully
• Multiple expired recordings cleaned in one pass
• File-backed attachments without expiresAt are never cleaned

Architecture docs

• QA Recording data flow section added
• File-backed attachment storage table
• Retention cleanup documentation
• Storage Summary table updated with file-backed attachment row

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 4 additional findings.

[chatgpt-codex-connector]

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[Jasonnnz]

Addressed in #6925