feat(web/ui): consolidate dialogs, cards, and breakpoints (Pass 3)

- Unify modal/dialog system; .modal-* are now aliases of .dialog-*
- Migrate WorkspacesPage, start-tool-modal, merge-dialog, workspace-tools-panel to .dialog-*
- Add .card-sm/.card-md/.card-lg/.card-elevated/.card-borderless modifiers
- Apply card utilities across workspaces, projects, ssh-keys, workspace-detail, git-history
- Remove duplicated card-like background/border/padding from page CSS
- Remove 860px breakpoint; standardize on 767px/768px mobile split
- Add docs/development/ui-review-checklist.md
- Archive web-ui-spacing-typography-rework OpenSpec change

apps/web/src/components/features/tool/instance-list.tsx

@@ -255,7 +255,7 @@ export const InstanceList = ({
 			) : (
 				<div className="instance-grid">
 					{instances.map((instance) => (
-						<div key={instance.id} className="instance-card">
+						<div key={instance.id} className="card card-md instance-card">
 							<LoadingOverlay
 								visible={busyInstanceId === instance.id}
 								label={busyLabel}