Add Codex repo-specific tracking structure

Codex/API/OPEN_ITEMS.md

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+# API — Open Items
+
+Only keep unfinished API work here.
+
+## Active
+- normalize backup response shape now that callers tolerate multiple field names
+- simplify and harden `devProxy`
+- service discovery migration for remaining hot-path references
+- provisioning validation follow-up where API behavior is involved
+- Headscale auth key generation
+
+## Verify before re-opening
+- hosted IDE token + hosted URL flow
+- backup forwarding semantics
+- readiness polling/cache behavior
+- quota enforcement on create flow
+
+## Not API-owned
+- agent-local backup implementation details
+- portal-only UX/polish
+- PBS / infra backup strategy