feat: add explicit completion wake policies

[valencia21]

Summary

• add per-job wake: never | failure | always completion policies
• persist and display wake policy across session reconstruction
• keep toast/widget updates independent from model-turn wakes
• add layered defaultWake / PI_BGRUN_WAKE configuration
• make foreground execution the documented default for routine focused commands

The package default remains always for backward compatibility; users can set defaultWake: "never" for opt-in model turns.

Verification

• bun run lint
• bun test extension/index.test.ts (195 passing)