Guard invalid route return values with ctx.json guidance

[isiliconx]

Summary

• Add a shared guard for unsupported route return values before response serialization reads .status or uses the in operator
• Reuse the existing ctx.json({...}) guidance for raw objects and invalid primitive/function/null/undefined returns
• Add regression coverage for undefined, null, string, number, boolean, bigint, symbol, and function returns

Testing

• npm test -- tests/errors/do-not-allow-raw-json.test.ts
• npm run typecheck
• npx prettier --check src/create-with-winter-spec.ts src/middleware/with-response-object-check.ts src/middleware/route-return-value-error.ts tests/errors/do-not-allow-raw-json.test.ts
• git diff --check

Note: on Windows, npm run build/pretest can prompt if dist already exists because the repo uses del dist; I removed only this repo's dist directory before rerunning checks.

/claim #30

AI-assisted; I reviewed the patch and verification results.

[isiliconx]

Quick status check on this one: the invalid route return guard is still open/mergeable, the Bun test workflow is green, and the Algora claim is still pending.

Happy to adjust the approach if you want this handled differently before merge.

[isiliconx]

Follow-up status: this PR is still open/mergeable, and the current head's Run Tests with Bun workflow is passing. The Algora claim page is still showing Total paid $0 / Status Pending.

Happy to make any final adjustments needed for merge.