fix: include method and path in plain object return error

[immanuwell]

What

When a route returns a plain object instead of ctx.json({...}), the error message now includes the HTTP method and path so it's immediately clear which route caused the problem.

Before:

Use ctx.json({...}) instead of returning an object directly.

After:

Route GET /api/foo returned a plain object. Use ctx.json({...}) instead of returning an object directly.

Changes

• src/middleware/with-response-object-check.ts: extract req.method and new URL(req.url).pathname and prepend them to the error message
• tests/errors/do-not-allow-raw-json.test.ts: add assertion that error includes "Route GET /"

/claim #30