[umpireboulianne-design]

Summary

• Add isJsonContentType(), checkAppraisalContentType(), and APPRAISAL_UNSUPPORTED_MEDIA_TYPE in services/appraisal-api/src/body-limit.ts and enforce Content-Type: application/json (accepting optional UTF-8 charset parameters such as application/json; charset=utf-8 case-insensitively) on POST /appraise in services/appraisal-api/src/server.ts.
• Return a stable 415 Unsupported Media Type JSON response ({ "error": "unsupported_media_type", "expected": "application/json" }) before reading the body or issuing a 402 quote when Content-Type is missing or non-JSON.
• Add unit and HTTP server tests in services/appraisal-api/src/body-limit.test.ts and update services/appraisal-api/README.md.

Supply-chain review

• No package scripts or dependencies changed. If changed, explain why below.
• No .vscode/, workflow, or other editor/config file changes. If changed, list them below.
• No lockfile changes. If changed, explain the update below.
• No binary or font asset changes. If changed, list and justify them below.
• I confirm no automatic task (such as preinstall/postinstall) was added.
• I confirm no hidden executable payload (encoded blob, obfuscated command, or unexpected binary) was added.
• Any changed executable or binary was reviewed by a maintainer.

Testing

• node --import tsx/esm --test services/appraisal-api/src/body-limit.test.ts services/appraisal-api/src/appraisal.test.ts services/appraisal-api/src/appraisal-fixtures.test.ts services/appraisal-api/src/config.test.ts

Closes #537
Fixes #537