Problem
Several accessibility issues found in the audit:
`SplitPane` drag handle not keyboard-accessible (suppressed a11y warning)
`CommandPalette` and `QuickSwitcher` lack focus traps and `role="dialog"`
Settings form labels not properly associated (missing `for`/`id`)
Entry toolbar lacks `role="toolbar"` grouping
Icon-only buttons have inconsistent `aria-label` vs `title` usageSolution
Add keyboard support to SplitPane (arrow keys to resize)
Add focus trap and proper ARIA to modal overlays
Wire up `for`/`id` on Settings form labels
Add `role="toolbar"` to entry edit toolbar
Audit all icon buttons for consistent `aria-label`Subsumes the aria-label items from the original `ux-accessibility-fixes` backlog item.