- Move inline DTOs to GmailDtos.cs, pure parse helpers to GmailParsing.cs
- Batch per-message existence checks in CreateSuggestedJob/RefreshLinkedThreads
- Remove redundant second pass in RelinkThread, reuse existing HashSet
- Replace ToListAsync+scan with FirstOrDefaultAsync for GmailReviewDecisions lookups
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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