feat(devkitd): manage durable agents in devkitd #414

Part of the devkitd agent migration (#406). Target: durable agents managed by devkitd — port DurableAgentRepository into daemon.db.

Scope

• durable_agents / durable_runs tables — port repository schema (state, session health, active run, last result)
• durable.create / list / show / send / stop RPCs
• durable.run — daemon spawns print-mode provider CLIs (claude -p, codex exec, pi); run pids observed by the existing sweep
• CLI: agent start --mode durable, agent send --id, agent session/sessions durable entries → daemon routing
• Durable launch commands in start_profiles (claude -p vs interactive argv)

Acceptance

• Durable create/send/session flows daemon-backed
• Run status reconciles (exit code → succeeded/failed/interrupted)