fix: implement T key for counter-clockwise rotation on selected nodes

[nnhhoang]

Summary

• The keyboard shortcuts dialog documents T as "Rotate item counter-clockwise by 90 degrees"
• T already works during placement/move mode (use-placement-coordinator.tsx, move-roof-tool.tsx)
• But pressing T on an already selected node did nothing — only R (clockwise) worked
• This adds the missing T handler in use-keyboard.ts matching the existing R handler pattern

Steps to reproduce (before fix)

Select item/door/window → press R → rotates clockwise → press T → nothing happens

After fix

Select item/door/window → press R → rotates clockwise → press T → rotates counter-clockwise

Test plan

• Select a placed item → press T → rotates counter-clockwise by 45 degrees
• Select a placed item → press R → still rotates clockwise
• Select a roof node → press T → rotates counter-clockwise
• T key ignored when typing in input fields (existing guard at line 11)
• T key still works during placement mode (unchanged code path)