feat(github): add observe-first repository onboarding

[osnucleo-ai]

Closes #26.

What changed

Introduces observe-first onboarding for existing repositories so teams can connect Facility without changing their established delivery workflow.

• Adds project-level observe and active autonomy modes.
• Keeps newly connected repositories quiet by default.
• Supports silent, summary, and live GitHub feedback modes.
• Prevents scheduled architect and learning agents from running until explicitly enabled.
• Keeps execution_lane as the existing safety control while exposing it in project settings.
• Adds configurable command namespacing, including commands such as /fx architect.
• Preserves project autonomy settings when repositories are connected or kickstarted.
• Adds project settings UI for autonomy mode, GitHub feedback, execution lane, schedules, and command prefix.
• Documents observe-first onboarding and least-privilege GitHub App permissions.
• Adds policy, scheduler, routing, authorization, and API coverage.

Why

Teams with a working SDLC should be able to evaluate Facility without allowing it to create comments, assignments, scheduled work, or pull requests before they deliberately opt in.

This creates a progressive adoption path:

1. Connect a repository.
2. Observe the project quietly.
3. Review plans in Facility.
4. Enable selected agent lanes or GitHub feedback.
5. Move to active automation when the team is ready.

Validation

Completed:

• git diff --check
• TypeScript syntax checks for changed files using Node 24
• Direct smoke validation of the project policy helpers
• Remote comparison against main: 19 files, 687 additions, 40 deletions

Not completed:

• pnpm verify could not run because the workspace dependencies were unavailable in the execution environment and package installation was blocked by network restrictions.