[mob][photos] Fix: FileAppbar buttons not working on some screens (#5022)

## Description

The Appbar was getting cut off at the bottom, likely due to a larger top
inset on certain screens, which makes the AppBar buttons unclickable
(have received reports on the favourite button being unclickable).

This change ensures that the Appbar remains useable on all screens. 

#### Before  
<img
src="https://github.com/user-attachments/assets/9611aae5-0671-4767-b5b6-22bac1f9d8f3"
width="320">



#### After  
<img
src="https://github.com/user-attachments/assets/8a360440-1d92-4168-a0e6-b8151b2a2788"
width="320">

mobile/lib/ui/viewer/file/custom_app_bar.dart

@@ -1,25 +0,0 @@
-import 'package:flutter/material.dart';
-
-class CustomAppBar extends PreferredSize {
-  @override
-  final Widget child;
-  @override
-  final Size preferredSize;
-  final double height;
-
-  const CustomAppBar(
-    this.child,
-    this.preferredSize, {
-    Key? key,
-    this.height = kToolbarHeight,
-  }) : super(key: key, child: child, preferredSize: preferredSize);
-
-  @override
-  Widget build(BuildContext context) {
-    return Container(
-      height: preferredSize.height,
-      alignment: Alignment.center,
-      child: child,
-    );
-  }
-}

mobile/lib/ui/viewer/file/detail_page.dart

@@ -156,7 +156,6 @@ class _DetailPageState extends State<DetailPage> {
               return FileAppBar(
                 _files![selectedIndex],
                 _onFileRemoved,
-                100,
                 widget.config.mode == DetailPageMode.full,
                 enableFullScreenNotifier: _enableFullScreenNotifier,
               );

mobile/lib/ui/viewer/file/file_app_bar.dart

@@ -23,7 +23,6 @@ import "package:photos/services/local_authentication_service.dart";
 import "package:photos/services/preview_video_store.dart";
 import "package:photos/theme/ente_theme.dart";
 import 'package:photos/ui/collections/collection_action_sheet.dart';
-import 'package:photos/ui/viewer/file/custom_app_bar.dart';
 import "package:photos/ui/viewer/file_details/favorite_widget.dart";
 import "package:photos/ui/viewer/file_details/upload_icon_widget.dart";
 import 'package:photos/utils/dialog_util.dart';
@@ -35,14 +34,12 @@ import 'package:photos/utils/toast_util.dart';
 class FileAppBar extends StatefulWidget {
   final EnteFile file;
   final Function(EnteFile) onFileRemoved;
-  final double height;
   final bool shouldShowActions;
   final ValueNotifier<bool> enableFullScreenNotifier;
 
   const FileAppBar(
     this.file,
     this.onFileRemoved,
-    this.height,
     this.shouldShowActions, {
     required this.enableFullScreenNotifier,
     super.key,
@@ -98,8 +95,9 @@ class FileAppBarState extends State<FileAppBar> {
 
     final isTrashedFile = widget.file is TrashFile;
     final shouldShowActions = widget.shouldShowActions && !isTrashedFile;
-    return CustomAppBar(
-      ValueListenableBuilder(
+    return PreferredSize(
+      preferredSize: const Size.fromHeight(kToolbarHeight),
+      child: ValueListenableBuilder(
         valueListenable: widget.enableFullScreenNotifier,
         builder: (context, bool isFullScreen, child) {
           return IgnorePointer(
@@ -124,32 +122,33 @@ class FileAppBarState extends State<FileAppBar> {
               stops: const [0, 0.2, 1],
             ),
           ),
-          child: AnimatedSwitcher(
-            duration: const Duration(milliseconds: 250),
-            switchInCurve: Curves.easeInOut,
-            switchOutCurve: Curves.easeInOut,
-            child: AppBar(
-              clipBehavior: Clip.none,
-              key: ValueKey(isGuestView),
-              iconTheme: const IconThemeData(
-                color: Colors.white,
-              ), //same for both themes
-              leading: IconButton(
-                icon: const Icon(Icons.arrow_back),
-                onPressed: () {
-                  isGuestView
-                      ? _requestAuthentication()
-                      : Navigator.of(context).pop();
-                },
+          child: SafeArea(
+            child: AnimatedSwitcher(
+              duration: const Duration(milliseconds: 250),
+              switchInCurve: Curves.easeInOut,
+              switchOutCurve: Curves.easeInOut,
+              child: AppBar(
+                clipBehavior: Clip.none,
+                key: ValueKey(isGuestView),
+                iconTheme: const IconThemeData(
+                  color: Colors.white,
+                ), //same for both themes
+                leading: IconButton(
+                  icon: const Icon(Icons.arrow_back),
+                  onPressed: () {
+                    isGuestView
+                        ? _requestAuthentication()
+                        : Navigator.of(context).pop();
+                  },
+                ),
+                actions: shouldShowActions && !isGuestView ? _actions : [],
+                elevation: 0,
+                backgroundColor: const Color(0x00000000),
               ),
-              actions: shouldShowActions && !isGuestView ? _actions : [],
-              elevation: 0,
-              backgroundColor: const Color(0x00000000),
             ),
           ),
         ),
       ),
-      Size.fromHeight(Platform.isAndroid ? 84 : 96),
     );
   }
 
@@ -179,10 +178,7 @@ class FileAppBarState extends State<FileAppBar> {
     }
     if (!isFileHidden && isFileUploaded) {
       _actions.add(
-        Padding(
-          padding: const EdgeInsets.all(8),
-          child: FavoriteWidget(widget.file),
-        ),
+        Center(child: FavoriteWidget(widget.file)),
       );
     }
     if (!isFileUploaded) {