feat(dashboard): zoom canvas with ctrl+scroll

[WhiteMuush]

Summary

• Ctrl/Cmd + scroll zooms the dashboard canvas (uniform CSS transform scale, 50%-200%)
• Whole grid + widget content scale together, no clipping
• Continuous zoom factor for fine control
• Gated on the physical Ctrl/Cmd key (tracked via keydown/keyup) so a trackpad pinch and plain scroll don't trigger it
• Forced to 1x while editing so RGL drag/resize pointer math stays correct; persisted layout never touched

Test plan

• Ctrl + scroll zooms in/out smoothly
• Plain scroll and trackpad pinch just scroll, no zoom
• Switching to Customize resets to 100% and drag/resize work