[codex] add Codex-native automation prompt

[ScriptedAlchemy]

Summary

Adds a simple Codex-native automation setup path to TraceDecay:

• tracedecay install --agent codex --automation prints a Codex-native automation request after installing the Codex plugin.
• The flow relies on Codex's own automation support instead of creating a TraceDecay-owned scheduler or automation directory.
• The generated request scopes the automation to the current project while using the user/profile-level TraceDecay store.

Notes

Codex's documented automation write path is in-app: ask Codex in a normal thread to create or update a standalone or thread automation. The public app-server docs do not expose a stable automation-create API for external installers, so this avoids writing private Codex app state or cron state.

Validation

• cargo test --lib codex_native_automation_prompt_uses_codex_owned_scheduler
• cargo test --all-targets codex_install_automation_flag_parses_without_extra_knobs
• cargo test --bin tracedecay startup_tests
• rg -n "crontab|codex_automation_root|CodexAutomation|install_codex_automation|codex_automation_script|\\.tracedecay/automations|backed by cron" src/agents/codex.rs src/main.rs src/cli.rs codex-plugin tests/agent_test.rs (no matches)
• git diff --check

[changeset-bot]

⚠️ No Changeset found

Latest commit: c7ed422

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR