- Add role=dialog and aria-modal attributes to all modal dialogs for accessibility
- Standardize close button aria-labels across all modals
- Unify overlay backdrop-filter, z-index, and background styles in styles.css
- Add light theme overrides for non-standard overlay backgrounds
- Update AgentListModal tests to reflect new aria attributes
- Add changeset for @gsxdsm/fusion package
- Create ChangesDiffModal component with unified/split diff views, syntax highlighting, and file stats
- Add expand button to TaskChangesTab to open changes in full-screen modal
- Add comprehensive CSS styles for diff modal, line numbers, and responsive layout
- Add full test coverage for ChangesDiffModal (rendering, diff modes, navigation, keyboard shortcuts)
- Add expand button tests to TaskChangesTab test suite
