feat(agent): add Codex print mode

[codeaholicguy]

Summary

• generalize print agents into a Claude/Codex discriminated union with atomic provider-session binding and legacy store migration
• add Codex CLI capability probing, JSONL runner, print-agent service, classified errors, and bounded parsing
• wire agent start/send/list/detail for --type codex --mode print without changing interactive Codex or Claude print behavior
• add a fake Codex fixture, unit/integration/CLI coverage, and all five AI lifecycle documents

Session identity

Codex agents are created with no provider thread ID. The first successful thread.started event is atomically bound before later output is accepted; subsequent sends resume that exact UUID. Conflicting or malformed identity is rejected.

Verification

• npx ai-devkit@latest lint --feature codex-print-mode
• npm run lint
• npm run build
• npm test
• agent-manager coverage: 28 files / 527 tests; new Codex pure logic has 100% line and function coverage, with the probe at 100% across all metrics
• CLI suite: 79 files / 932 tests

Deferred

• Pi print mode
• additional capacity/concurrency policy beyond the existing print-agent model