Nudge: Arrow keys move selection by 1px, Shift+Arrow by 10px.
Consecutive nudges within 300ms are batched into a single undo
entry so Cmd+Z undoes the entire sequence at once.
Fix duplicate redo creating nodes with new IDs, breaking
subsequent undo entries that reference the original IDs. Now
snapshotSubtree/restoreSubtree preserve node IDs across redo.
Fix delete undo not restoring children — deleteSelected only
snapshotted top-level nodes, so undoing a frame delete lost all
its children. Now snapshots the full subtree.
Fix draw tool not committing resize to undo — shapes created via
draw had their final dimensions lost on redo because handleDrawUp
never recorded the resize. Now uses beginBatch/commitBatch to
combine create+resize into a single undo entry.
Clean up use-keyboard.ts — remove shouldPreventDefault and opaque
PREVENT_* sets, move tool switch and nudge to dedicated keydown
listener, add shift() helper.
Closes#182
