Window Snapping: Add UI to Active Rules tab

[malpern]

Problem

Window Snapping collection exists and works, but UI is only in Summary tab, not in Active Rules tab where users expect to configure it.

Status

• Config: Two conventions (Standard/Vim), mappings complete
• Backend: 13 window actions working (left/right halves, corners, maximize, center, undo)
• Missing: No WindowSnappingCollectionView

Impact

Feature works but can't be configured from Rules UI where users look for it.

Fix

1. Create WindowSnappingCollectionView
2. Add to ActiveRulesView rendering
3. Enable by default OR add discovery mechanism

References

• Comprehensive review: docs/code-review/comprehensive-feature-review.md section 3.1