feat: enforce 44px minimum touch targets for receipt OCR components (refs #140)

Adds minHeight/minWidth: 44 to ReceiptCameraButton, ReceiptOcrReviewModal
action buttons, and UpgradeRequiredDialog buttons and close icon to meet
mobile accessibility requirements.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/features/fuel-logs/components/ReceiptCameraButton.tsx

@@ -48,6 +48,8 @@ export const ReceiptCameraButton: React.FC<ReceiptCameraButtonProps> = ({
             size={size}
             aria-label={locked ? 'Scan receipt (Pro feature)' : 'Scan receipt with camera'}
             sx={{
+              minWidth: 44,
+              minHeight: 44,
               backgroundColor: locked ? 'action.disabledBackground' : 'primary.light',
               color: locked ? 'text.secondary' : 'primary.contrastText',
               '&:hover': {
@@ -77,6 +79,7 @@ export const ReceiptCameraButton: React.FC<ReceiptCameraButtonProps> = ({
           startIcon={locked ? <LockOutlinedIcon /> : <ReceiptIcon />}
           endIcon={locked ? undefined : <CameraAltIcon />}
           sx={{
+            minHeight: 44,
             borderStyle: 'dashed',
             '&:hover': {
               borderStyle: 'solid',

frontend/src/features/fuel-logs/components/ReceiptOcrReviewModal.tsx

@@ -430,14 +430,14 @@ export const ReceiptOcrReviewModal: React.FC<ReceiptOcrReviewModalProps> = ({
         <Button
           onClick={onRetake}
           startIcon={<CameraAltIcon />}
-          sx={{ order: isMobile ? 2 : 1 }}
+          sx={{ order: isMobile ? 2 : 1, minHeight: 44 }}
         >
           Retake Photo
         </Button>
         <Box sx={{ flex: 1, display: isMobile ? 'none' : 'block' }} />
         <Button
           onClick={onCancel}
-          sx={{ order: isMobile ? 3 : 2 }}
+          sx={{ order: isMobile ? 3 : 2, minHeight: 44 }}
         >
           Cancel
         </Button>
@@ -445,7 +445,7 @@ export const ReceiptOcrReviewModal: React.FC<ReceiptOcrReviewModalProps> = ({
           variant="contained"
           onClick={onAccept}
           startIcon={<CheckIcon />}
-          sx={{ order: isMobile ? 1 : 3, width: isMobile ? '100%' : 'auto' }}
+          sx={{ order: isMobile ? 1 : 3, width: isMobile ? '100%' : 'auto', minHeight: 44 }}
         >
           Accept
         </Button>