fix: add keyboard focus trap and return focus to modals

[Odunsih1]

fix: add keyboard focus trap and return focus to modals
What this fixes
Modals lacked a proper keyboard focus trap, meaning Tab could escape the dialog and interact with elements behind it. Additionally, focus was not returned to the triggering element after a modal closed.
Changes

Added src/hooks/use-focus-trap.ts, a shared hook that handles:

Trapping Tab/Shift+Tab within the open dialog
Capturing the triggering element on open and returning focus to it on close

Applied the hook to all four modals:

NewCanvasDialog
DeleteConfirmDialog
EditorShortcutsModal
ImageCropModal

Accessibility impact

Tab and Shift+Tab now cycle only through focusable elements inside the open modal
Closing any modal (via Escape, Cancel, backdrop click, or confirm) returns focus to the element that opened it
Consistent behavior across all modals via a single reusable hook

Before:

Video.Project.1.mp4

After:

Video.Project.2.mp4

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