Touch-target audit: 44px minimum on mobile interactive elements (Slice 9)

Apply the mobile-touch-target CSS class to 40 interactive elements across
12 files. The class applies min-height/min-width:44px only below md
(max-width:767px), satisfying WCAG 2.5.5 / Apple HIG on touch devices.
Desktop behavior is unchanged.

Audit log (before -> after hit-area):
- App.tsx: hamburger/dark-mode/sign-out (32/32/28 -> 44)
- Dashboard.tsx: shortcut open/edit/delete (28 -> 44), enabled switch (18 -> 44)
- Media.tsx: mobile pagination prev/next (28 -> 44)
- FileBrowser.impl.tsx: 'Open Settings' alert button (28 -> 44)
- UsersPage.impl.tsx: compose toolbar bold/italic/link/list (32 -> 44),
  attachment remove button (16 -> 44)
- Settings.tsx: machine switch (18 -> 44), clear/add-machine buttons (28 -> 44),
  reset-db checkboxes x3 (16 -> 44)
- Actions.tsx: 'Add action' button (28 -> 44)
- ServicePage.tsx: service enabled switch (18 -> 44)
- ServicesPage.tsx: service switch/open-link/delete-icon (18/28/32 -> 44)
- ObservabilityPage.tsx: retry + 4 asChild link buttons (28 -> 44)
- WidgetConfigDialog.tsx: 4 icon buttons (32 -> 44), 2 switches (18 -> 44),
  2 add-widget buttons (28 -> 44)
- SessionActivityPanel.tsx: 'Open in Users' button (28 -> 44)

Deliberately skipped: default-size text buttons (32px, borderline), desktop-only
sidebar toggle, DataTable internals (desktop-only below md), Select triggers.
Dashboard anchor pills and HoverEditButton already had the class from Slices 1/2.

No new tests (the class applies via @media which jsdom doesn't honor).
116 tests pass; lint/build green.

Refs openspec/changes/mobile-responsive-parity/ (spec R6, tasks slice 9).

frontend/src/components/WidgetConfigDialog.tsx

@@ -315,6 +315,7 @@ export function WidgetConfigDialog({ open, onClose }: Props) {
 			<div className="flex items-center gap-2">
 				<Switch
 					id="widget-enabled"
+				className="mobile-touch-target"
 					checked={draft.enabled}
 					onCheckedChange={(checked) =>
 						setDraft({ ...draft, enabled: checked })
@@ -377,7 +378,7 @@ export function WidgetConfigDialog({ open, onClose }: Props) {
 									<Button
 										variant="ghost"
 										size="icon"
-										className="h-8 w-8"
+										className="mobile-touch-target h-8 w-8"
 										disabled={index === 0}
 										onClick={() => moveInstance(index, -1)}
 									>
@@ -386,21 +387,22 @@ export function WidgetConfigDialog({ open, onClose }: Props) {
 									<Button
 										variant="ghost"
 										size="icon"
-										className="h-8 w-8"
+										className="mobile-touch-target h-8 w-8"
 										disabled={index === sortedInstances.length - 1}
 										onClick={() => moveInstance(index, 1)}
 									>
 										<ChevronDown className="h-4 w-4" />
 									</Button>
 									<Switch
-										checked={instance.enabled}
+							className="mobile-touch-target"
+								checked={instance.enabled}
 										onCheckedChange={() => toggleEnabled(instance)}
 										aria-label={`Toggle ${instance.title}`}
 									/>
 									<Button
 										variant="ghost"
 										size="icon"
-										className="h-8 w-8"
+										className="mobile-touch-target h-8 w-8"
 										onClick={() => startEdit(instance)}
 									>
 										<Pencil className="h-4 w-4" />
@@ -408,7 +410,7 @@ export function WidgetConfigDialog({ open, onClose }: Props) {
 									<Button
 										variant="ghost"
 										size="icon"
-										className="h-8 w-8 text-destructive"
+										className="mobile-touch-target h-8 w-8 text-destructive"
 										onClick={() => removeInstance(instance)}
 									>
 										<Trash2 className="h-4 w-4" />
@@ -428,6 +430,7 @@ export function WidgetConfigDialog({ open, onClose }: Props) {
 							key={b.kind}
 							variant="outline"
 							size="sm"
+							className="mobile-touch-target"
 							onClick={() => startAddBuiltIn(b.kind)}
 						>
 							<Plus className="mr-1 h-3 w-3" />
@@ -442,6 +445,7 @@ export function WidgetConfigDialog({ open, onClose }: Props) {
 									key={`${s.id}:${w.kind}`}
 									variant="outline"
 									size="sm"
+									className="mobile-touch-target"
 									onClick={() => startAddService(s.id, w.kind)}
 								>
 									<Plus className="mr-1 h-3 w-3" />