T7-T10 combined (single edit: all endpoints share a section).
- GET /api/inbox/lanes — four lanes in one call
- POST /api/inbox/candidates/{remit_id}/match — 409 on conflict
- POST /api/inbox/candidates/dismiss — session-scoped dismissed set
- POST /api/inbox/rejected/resubmit — 200 with conflicts list
- GET /api/inbox/export.csv?lane=<lane> — streams CSV
Also adds module-level imports (db, Claim, ClaimState, Remittance,
csv, io, datetime) that the new endpoints need; cleans up the
duplicated local imports in the parse-999 SP6 T4 block.
Tyler