test: add list and delete route test coverage

[Furox-Art]

Closes #2
/claim #2

Disclosure: This PR was authored by @Furox-Art (AI-assisted). Happy to adjust anything.

Summary

Adds the missing route test coverage for things/list and things/delete,
following the established getTestServer + ky fixture pattern, and fixes the
un-awaited create request on the existing test.

New tests — tests/routes/things/list.test.ts

• Empty list returns { things: [] } before anything is created
• All created things are returned with thing_id/name/description in
  creation order, and thing_id values are unique
• A fresh server instance reflects only its own state (no cross-test leakage)

New tests — tests/routes/things/delete.test.ts

• Deleting a specific thing removes exactly that thing from the list
• Deleting one of several keeps the others intact (verifies thing_id
  matching, not just count)
• Deleting a non-existent thing_id still returns { ok: true } and leaves
  the list unchanged (documents current idempotent behavior)
• Deleting the same thing twice succeeds without error

Fix — tests/routes/things/create.test.ts

• ky.post is now awaited (the un-awaited request could race the subsequent
  list assertion) and the { ok: true } response + created fields are
  asserted

Notes

• Delete requests use new URLSearchParams(...) bodies, matching the
  application/x-www-form-urlencoded contract of the route spec.
• All response assertions use explicit json<{ ok: boolean }>() typing so
  tsc --noEmit stays clean.

Verification

• bun test tests/routes/ → 9 pass, 0 fail (2 existing + 7 new)
• tsc --noEmit → no errors in tests/
• biome format clean on all touched files

[Furox-Art]

Withdrawing — the linked bounty (#2) is already marked 💰 Rewarded and has several competing PRs. Closing to keep the queue clean.