Touch-target pass: 44px min on default-size buttons (WCAG 2.5.5)

Applies .mobile-touch-target to 32 default-size <Button> elements (32px
tall, below the mobile minimum) across 9 files for strict WCAG 2.5.5
compliance: Save, Cancel, Delete, Validate SSH, Run job, Build index,
Update connection, Add service, etc. Plus the shared DialogFooter Cancel
+ Confirm buttons (used by every ConfirmDialog).

The class applies min-height/min-width: 44px only below md
(max-width: 767px); no-op at md+, so desktop sizing is unchanged.

Completes the touch-target audit started in Slice 9 (which covered icon
buttons, size=sm buttons, checkboxes, switches). 122 tests pass; lint/
build green. No new tests (@media queries aren't honored by jsdom).

Refs openspec/changes/mobile-responsive-parity/verify-report.md residual
risk #2.

frontend/src/components/WidgetConfigDialog.tsx

@@ -332,10 +332,10 @@ export function WidgetConfigDialog({ open, onClose }: Props) {
 			/>
 			{!isMobile ? (
 				<div className="flex justify-end gap-2">
-					<Button variant="outline" onClick={reset}>
+					<Button variant="outline" onClick={reset} className="mobile-touch-target">
 						Back
 					</Button>
-					<Button onClick={saveDraft} disabled={saveWidget.isPending}>
+					<Button onClick={saveDraft} disabled={saveWidget.isPending} className="mobile-touch-target">
 						Save widget
 					</Button>
 				</div>