Shell repair engine

A three-tier shell repair for the acknowledged KB5072911 taskbar and Start bug, with per-tier snapshots.

• 3-tier shell repair for the KB5072911 bug Microsoft has acknowledged since July 2025: broken taskbar right-click, Start search closing Start, and taskbar search doing nothing
• Tier 1 re-registers the three CBS XAML host packages most forum fixes miss. Tier 2 runs the full DISM plus SFC integrity repair. Tier 3 is the Microsoft Solution 6 CBS state reset for deep corruption, with search history backup before anything is deleted
• Per-tier snapshots: each repair layer creates its own restore point so any tier can be undone separately
• May 2026 Patch Tuesday updates (KB5089549, KB5087420, KB5087544) recognized with build numbers and supersession chains
• Broad repair coverage across the most common Windows problems