Show 'last year', 'last week' and 'last month' headers in gallery when appropriate

mobile/apps/photos/lib/generated/intl/messages_en.dart

@@ -1195,8 +1195,11 @@ class MessageLookup extends MessageLookupByLibrary {
         "kindlyHelpUsWithThisInformation": MessageLookupByLibrary.simpleMessage(
             "Kindly help us with this information"),
         "language": MessageLookupByLibrary.simpleMessage("Language"),
+        "lastMonth": MessageLookupByLibrary.simpleMessage("Last month"),
         "lastTimeWithThem": m45,
         "lastUpdated": MessageLookupByLibrary.simpleMessage("Last updated"),
+        "lastWeek": MessageLookupByLibrary.simpleMessage("Last week"),
+        "lastYear": MessageLookupByLibrary.simpleMessage("Last year"),
         "lastYearsTrip":
             MessageLookupByLibrary.simpleMessage("Last year\'s trip"),
         "leave": MessageLookupByLibrary.simpleMessage("Leave"),

mobile/apps/photos/lib/generated/l10n.dart

@@ -12306,6 +12306,16 @@ class S {
     );
   }
 
+  /// `Last week`
+  String get lastWeek {
+    return Intl.message(
+      'Last week',
+      name: 'lastWeek',
+      desc: '',
+      args: [],
+    );
+  }
+
   /// `This month`
   String get thisMonth {
     return Intl.message(
@@ -12316,6 +12326,16 @@ class S {
     );
   }
 
+  /// `Last month`
+  String get lastMonth {
+    return Intl.message(
+      'Last month',
+      name: 'lastMonth',
+      desc: '',
+      args: [],
+    );
+  }
+
   /// `This year`
   String get thisYear {
     return Intl.message(
@@ -12326,6 +12346,16 @@ class S {
     );
   }
 
+  /// `Last year`
+  String get lastYear {
+    return Intl.message(
+      'Last year',
+      name: 'lastYear',
+      desc: '',
+      args: [],
+    );
+  }
+
   /// `Group by`
   String get groupBy {
     return Intl.message(

mobile/apps/photos/lib/l10n/intl_en.arb

@@ -1790,7 +1790,10 @@
   "cLDesc6": "No more waiting for uploads/downloads to complete before you can close the app. All uploads and downloads now have the ability to be paused midway, and resume from where you left off.",
   "indexingPausedStatusDescription": "Indexing is paused. It will automatically resume when the device is ready. The device is considered ready when its battery level, battery health, and thermal status are within a healthy range.",
   "thisWeek": "This week",
+  "lastWeek": "Last week",
   "thisMonth": "This month",
+  "lastMonth": "Last month",
   "thisYear": "This year",
+  "lastYear": "Last year",
   "groupBy": "Group by"
 }

mobile/apps/photos/lib/ui/viewer/gallery/component/group/type.dart

@@ -199,7 +199,15 @@ extension GroupTypeExtension on GroupType {
     if (startOfWeek.year == nowStartOfWeek.year &&
         startOfWeek.month == nowStartOfWeek.month &&
         startOfWeek.day == nowStartOfWeek.day) {
-      return "This week";
+      return S.of(context).thisWeek;
+    }
+
+    // Check if it's the previous week
+    final lastWeekStart = nowStartOfWeek.subtract(const Duration(days: 7));
+    if (startOfWeek.year == lastWeekStart.year &&
+        startOfWeek.month == lastWeekStart.month &&
+        startOfWeek.day == lastWeekStart.day) {
+      return S.of(context).lastWeek;
     }
 
     // Return formatted week range
@@ -212,7 +220,13 @@ extension GroupTypeExtension on GroupType {
     final now = DateTime.now();
 
     if (date.year == now.year && date.month == now.month) {
-      return "This month";
+      return S.of(context).thisMonth;
+    }
+
+    // Check if it's the previous month
+    final lastMonth = DateTime(now.year, now.month - 1);
+    if (date.year == lastMonth.year && date.month == lastMonth.month) {
+      return S.of(context).lastMonth;
     }
 
     return DateFormat.yMMM(Localizations.localeOf(context).languageCode)
@@ -224,7 +238,12 @@ extension GroupTypeExtension on GroupType {
     final now = DateTime.now();
 
     if (date.year == now.year) {
-      return "This year";
+      return S.of(context).thisYear;
+    }
+
+    // Check if it's the previous year
+    if (date.year == now.year - 1) {
+      return S.of(context).lastYear;
     }
 
     return DateFormat.y(Localizations.localeOf(context).languageCode)