Clear the HTTP handler quality gate

[jonbaldie]

Closes #35

What changed

• Split the HTTP handler into focused request-body, route-registration, payload-response, and logging helpers.
• Kept route behavior behind the existing public Request/Response seam.
• Replaced development-only console calls with direct Deno stdout/stderr writes.
• Centralized queue-name error translation and made payload response rendering reflect the JSON values the API already accepts.

Why

The handler's monolithic structure triggered messcript method-length, cyclomatic-complexity, naming, and development-code findings. This refactor clears that unit gate without weakening policy or changing documented endpoint behavior.

Validation

• npm run quality:unit -- http-handler
• deno lint src/handler.ts
• deno test --frozen=false --allow-all tests/handler_test.ts — 94 passed
• deno test --frozen=false --allow-all — 180 passed
• Two-axis review: Standards pass; Spec pass