test: await ky create request

[Isjuanplayer]

Summary

• await the ky POST in the create-route regression test before listing things
• assert the create response body is { ok: true }
• verify the created thing payload, including generated thing_id

Validation

• npx --yes bun test tests/routes/things/create.test.ts
• npx --yes bun x tsc --noEmit tests/routes/things/create.test.ts --types bun --moduleResolution bundler --module ESNext --target ESNext --baseUrl . --jsx preserve --allowImportingTsExtensions --noEmit --skipLibCheck
• npx --yes bun run build
• npx --yes bun x biome format tests/routes/things/create.test.ts

/claim #2