chore: versiona cartella android/ e pubspec.lock

Rende il repo clonabile e buildabile da chiunque senza passi manuali:
- android/ rimosso da .gitignore: contiene applicationId, label, icone
  e MainActivity con il package corretto (com.davide.biteplan)
- pubspec.lock aggiunto: necessario per --enforce-lockfile nella build
- File generati/macchina-specifici già esclusi da android/.gitignore
  (.gradle/, local.properties, GeneratedPluginRegistrant.java)

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

android/app/src/main/res/values-night/styles.xml

@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <!-- Theme applied to the Android Window while the process is starting when the OS's Dark Mode setting is on -->
+    <style name="LaunchTheme" parent="@android:style/Theme.Black.NoTitleBar">
+        <!-- Show a splash screen on the activity. Automatically removed when
+             the Flutter engine draws its first frame -->
+        <item name="android:windowBackground">@drawable/launch_background</item>
+    </style>
+    <!-- Theme applied to the Android Window as soon as the process has started.
+         This theme determines the color of the Android Window while your
+         Flutter UI initializes, as well as behind your Flutter UI while its
+         running.
+
+         This Theme is only used starting with V2 of Flutter's Android embedding. -->
+    <style name="NormalTheme" parent="@android:style/Theme.Black.NoTitleBar">
+        <item name="android:windowBackground">?android:colorBackground</item>
+    </style>
+</resources>