Use existing material localizations for "cancel" and use lower case for "add"

lib/l10n/app_en.arb

@@ -155,7 +155,6 @@
   "@category": {
     "description": "Category for an exercise, ingredient, etc."
   },
-  "endDate": "End date",
   "startDate": "Start date",
   "routines": "Routines",
   "newRoutine": "New routine",
@@ -778,12 +777,8 @@
   "@imageDetailsLicenseNoticeSuffix": {
     "description": "Second part of license notice text"
   },
-  "imageDetailsCancel": "CANCEL",
-  "@imageDetailsCancel": {
-    "description": "Cancel button text"
-  },
-  "imageDetailsAdd": "ADD",
-  "@imageDetailsAdd": {
+  "add": "add",
+  "@add": {
     "description": "Add button text"
   },
   "variations": "Variations",

lib/widgets/add_exercise/image_details_form.dart

@@ -323,7 +323,7 @@ class _ImageDetailsFormState extends State<ImageDetailsForm> {
       children: [
         TextButton(
           onPressed: widget.onCancel,
-          child: Text(AppLocalizations.of(context).imageDetailsCancel),
+          child: Text(MaterialLocalizations.of(context).cancelButtonLabel),
         ),
         const SizedBox(width: 8),
         ElevatedButton(
@@ -369,7 +369,7 @@ class _ImageDetailsFormState extends State<ImageDetailsForm> {
             padding: const EdgeInsets.symmetric(horizontal: 32, vertical: 12),
           ),
           child: Text(
-            AppLocalizations.of(context).imageDetailsAdd,
+            AppLocalizations.of(context).add,
             style: const TextStyle(fontWeight: FontWeight.bold, color: Colors.white),
           ),
         ),