Implement Context V2

[ethznn]

Summary

• Replace display-specific Space labels with a ContextPlan model that stores one name per shared Context.
• Migrate legacy DisplaySpacePlan labels into ContextPlan while keeping DisplaySpacePlan as migration input only.
• Add Context capture orchestration that aligns to the first Space, captures forward, and stops at the shortest selected display Space sequence.
• Drive switching, HUD, settings, and sync warnings from ContextPlan.
• Expand PR CI to build both app products after tests.

Testing

• swift test (237 tests, 0 failures)
• swift build --product SidebyApp
• swift build --product SidebyDevApp
• git diff --check
• Manual multi-display/Spaces QA not run yet; should be checked locally before release.

Checklist

• I kept the change focused.
• I updated tests for logic changes.
• I updated docs for user flow, architecture, permission, release, or packaging changes.
• I did not introduce private Mission Control or Spaces API usage.
• I did not change the App Sandbox off direct-distribution decision without maintainer approval.
• I did not add Screen Recording as a V1 requirement.

[ethznn]

Closed after manually squash-merging Context V2 into main as c22d305. The v0.2.0 release remains tagged at 97cfa2f with the notarized DMG attached.