No `Content-Type` Header Crashes Request

[thehabes]

JSON body with no Content-Type header will do it.

Load Test Evidence (Run 4, Phase 8 — Fuzzing)

From k6 Phase 8e (header manipulation):

• POST /v1/api/create with valid JSON body but no Content-Type header at all → 500
• k6 logged EOF error (connection closed unexpectedly), similar to Connection reset on bad headers #248

This and #245 likely share the same root cause: Express's express.json() middleware throws an unhandled error when it can't parse the body due to Content-Type mismatch/absence. A middleware guard before express.json() checking Content-Type would fix both.

Expected: 400 Bad Request or 415 Unsupported Media Type.