Mirrors the backend Pydantic `SyncResultOut` in TS so the mutation result is
properly typed end-to-end. `(res as { duration_ms: number })` cast removed
from MitrePage.tsx; `apiPost<MitreSyncResult>` carries the contract.
Also annotated the unused query-key factories in mitre.ts so the next reader
knows they're parked for M5 template-form consumption (not dead).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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