Ingest a CSDS snapshot file.

Runs the requested CSDS processor synchronously against an uploaded JSON snapshot rendered from the reporting pipeline. The processor key in the path must be one of application_codes, resolution_codes, fee, national_court_houses, or standard_applicants. Implemented processors must also be enabled in CSDS ingress configuration; disabled processors return 409 Conflict, and recognised but unimplemented processors return 501 Not Implemented. The endpoint honours the distributed CSDS ingest lock and returns 423 Locked if another run already owns it. The global 5MB multipart file limit applies.