test: cover ky form delete flow

[tonghuaxingdsb]

Summary

• add a ky-backed test for deleting a thing through the url-encoded form endpoint
• verify create -> list -> delete -> list so the migrated client covers POST form bodies
• remove an unused type import from the delete route

Verification

• bun test
• bun run build
• bun run typecheck
• bun x biome format routes/things/delete.ts tests/routes/things/delete.test.ts

/claim #2

EVM payout address if supported: 0x9f7fFAd83668829FbC80c0a9a64f8557D92cA1E6

[tonghuaxingdsb]

All checks are green and the bounty claim is linked. Happy to adjust the coverage shape if you'd prefer this exercised differently.