refactor: Remove AppTitleBar widget and its references from various screens

lib/screens/biometric_choice_screen.dart

@@ -1,5 +1,4 @@
 import 'package:flutter/material.dart';
-import 'package:notas/widgets/app_title_bar.dart';
 
 class BiometricChoiceScreen extends StatelessWidget {
   const BiometricChoiceScreen({
@@ -31,7 +30,6 @@ class BiometricChoiceScreen extends StatelessWidget {
         child: SafeArea(
           child: Column(
             children: [
-              const AppTitleBar(),
               Expanded(
                 child: Center(
                   child: SingleChildScrollView(

lib/screens/biometric_gate_screen.dart

@@ -1,5 +1,4 @@
 import 'package:flutter/material.dart';
-import 'package:notas/widgets/app_title_bar.dart';
 
 class BiometricGateScreen extends StatefulWidget {
   const BiometricGateScreen({
@@ -55,7 +54,6 @@ class _BiometricGateScreenState extends State<BiometricGateScreen> {
         child: SafeArea(
           child: Column(
             children: [
-              const AppTitleBar(),
               Expanded(
                 child: Center(
                   child: SingleChildScrollView(

lib/screens/note_editor_screen.dart

@@ -485,20 +485,17 @@ class _NoteEditorScreenState extends State<NoteEditorScreen> {
     return LayoutBuilder(
       builder: (BuildContext context, BoxConstraints constraints) {
         final double maxWidth = math.min(constraints.maxWidth - 32, 600);
-        final double maxHeight = math.min(constraints.maxHeight - 64, 720);
-        final double overlayTop = MediaQuery.paddingOf(context).top + 32;
+        final double maxHeight = math.min(constraints.maxHeight - 32, 720);
 
         return Stack(
           children: [
             Positioned.fill(
-              top: overlayTop,
               child: ModalBarrier(
                 dismissible: false,
                 color: const Color.fromARGB(54, 0, 0, 0).withValues(alpha: 0.5),
               ),
             ),
             Positioned.fill(
-              top: overlayTop,
               child: Center(
                 child: SizedBox(
                   width: maxWidth,

lib/screens/vault_access_screen.dart

@@ -1,5 +1,4 @@
 import 'package:flutter/material.dart';
-import 'package:notas/widgets/app_title_bar.dart';
 import 'package:notas/data/api_client.dart';
 
 class VaultAccessScreen extends StatefulWidget {
@@ -90,7 +89,6 @@ class _VaultAccessScreenState extends State<VaultAccessScreen> {
         child: SafeArea(
           child: Column(
             children: [
-              const AppTitleBar(),
               Expanded(
                 child: Center(
                   child: SingleChildScrollView(