fix: normalize adapter middleware responses

[charlie12520]

Summary

• Normalize responses returned by public makeRequest / adapter options.middleware.
• Thread makeRequest options through createWinterSpecFromRouteMap so the exported helper exercises the same middleware path.
• Normalize custom handle404 returns so raw JSON gets the existing guidance and ctx.json-style runtime returns become real Responses.
• Serialize ctx.json(...) / SerializableToResponse middleware short-circuits with z.any().
• Throw the existing raw JSON guidance when adapter middleware or handle404 returns a plain object.
• Throw a clear helper error when adapter middleware or handle404 returns unsupported primitives instead of passing invalid values through as Responses.
• Add focused regression coverage for adapter middleware and handle404 raw object / ctx.json / invalid return paths.

Acceptance / contributor review

• Reviewed issue When a user returns return { ... } from a route instead of return ctx.json({ ... }), throw an error telling them to use ctx.json #30 acceptance surface: unsupported raw route-style returns should produce the actionable ctx.json(...) guidance instead of confusing serialization errors.
• Reviewed CONTRIBUTING.md: it asks contributors to run AVA for specific test files or npm run test for the full suite.
• Checked open PRs before submission for makeRequest/options.middleware and custom handle404 raw JSON / ctx.json paths; I did not find an overlapping open PR.

Validation

• 2026-05-27 fresh check: npx ava tests/errors/do-not-allow-raw-json.test.ts -> 7 passed.
• Earlier check: npx ava tests/errors/do-not-allow-raw-json.test.ts -> 7 passed.
• Earlier check: npx prettier --check src/types/winter-spec.ts tests/errors/do-not-allow-raw-json.test.ts -> passed.
• Earlier check: git diff --check -> passed, with only the normal Windows LF-to-CRLF warning.
• npx tsc --noEmit --pretty false -> blocked by existing OpenAPI/codegen type errors in src/cli/commands/codegen/openapi.ts, src/cli2/commands/codegen/openapi.ts, and tests/cli/codegen/openapi/openapi-codegen.test.ts.
• npm test -- tests/errors/do-not-allow-raw-json.test.ts -> blocked during pretest build by the existing OpenAPI operation.responses errors above.

Non-overlap check

Before submitting, I checked open PRs for makeRequestAgainstWinterSpec middleware, adapter middleware ctx.json, options.middleware raw object, handle404 ctx.json, and handle404 raw JSON. I did not find an open PR covering these public makeRequest/options.middleware or handle404 paths. PR #162 covers route/auth middleware inside createWithWinterSpec; this patch covers adapter-level middleware and custom 404 handlers passed through makeRequest/adapters.

/claim #30