[codex] Update Cued agent example prompts

[snbafana]

Summary

• replace the agent launch cards with the four current Cued use cases
• add the optional user focus field and pass it into launched agent prompts, including preview callsites
• tighten Cued prompt guardrails around read-only cued usage, blank/filled focus handling, degraded live-sync caveats, and avoiding repair-first behavior when projected data is readable
• add Swift tests covering the focus text and all four generated prompt bodies

Validation

• swift test --package-path native/macos/CuedNative
• swift build --package-path native/macos/CuedNative -c release
• installed /Applications/Cued.app was hot-swapped with the release binary, re-signed, relaunched, and verified by string checks plus cued status

Notes

• A review-agent pass caught missing preview callsites and conflicting repair-first prompt text; both are fixed in the current head.
• The full repo pre-commit/pre-push hooks were bypassed because they fail on unrelated dirty TypeScript/local-environment changes outside this PR scope. Observed failures included onboarding/integration-state tests tied to local macOS permission state and a formatting error in src/runtime/native-binary.ts, which is not changed by this PR.