Reconcile Gmail label state during sync

[bberenberg]

Summary

• split the Gmail sync label reconciliation work out of Adds codex support, Adds multi account view, small perf and security fixes #92 into a focused PR
• reconcile inbox label state against current Gmail labels during sync so archived and read state stop drifting locally
• harden the new reconciliation path against duplicate history events and fragile inbox label matching

Changes

• reconcile visible inbox label state during sync using current Gmail labels
• deduplicate newMessageIds before fetching message bodies during incremental sync
• replace substring-based inbox label checks in the new reconciliation helpers with json_each membership checks
• add focused unit coverage for the new dedupe and inbox label matching behavior

Tests

• npx tsc --noEmit
• npm run test:unit -- database
• npm run test:unit -- email-sync

Split from #92.