Add an optional ``?download=true`` query param to
``POST /api/inbox/rejected/resubmit`` that returns the same operation
result as a ZIP archive of regenerated 837P files (one
``claim-{id}.x12`` per successfully resubmitted claim) rather than the
JSON envelope.
Why: operators who mass-resubmit rejected claims want to hand the
files straight to their clearinghouse; round-tripping through copy-
paste is error-prone.
Implementation notes:
* Uses ``serialize_837_for_resubmit`` so each X12 file in the bundle
gets a unique interchange/group control number (back-to-back
resubmits would otherwise collide on ISA13/GS06 = "000000001").
* Conflicts and missing ids are deliberately excluded from the ZIP
— the user already saw them in the JSON path on prior calls; the
download is the "give me the files I asked for" payload.
* Empty resubmit + download returns 200 with an empty ZIP so the UI
can still hand the user a downloadable artifact.
Tests (test_inbox_endpoints.py): 2 new tests covering the success
shape (one .x12 per accepted claim) and the conflict-exclusion
contract.
Tyler
ec9eae7a2c