Fix Codex app touchpad cycling from the active project

[stephenleo]

Summary

• initialize the Codex Desktop chat-cycle cursor from the most recently active thread
• advance immediately to the next chat in that project
• add regression coverage for a newer-created singleton project masking the active multi-chat project

Root cause

The cold cursor assumed the first UUID-creation-ordered catalog row was frontmost. A newer one-off task therefore scoped Touchpad cycling to its single-thread cwd forever, even while another project was active.

Verification

• npx vitest run test/harness.test.ts — 28/28 passed
• npm run verify — 269/269 passed; typecheck, lint, and format check passed
• npm run build — passed
• direct exported-harness reproduction now returns two different same-project thread deep links (cycled: true)

No release/version change is included.