chore: housekeeping cleanup and code deduplication

- Remove stray tracked files (root AndroidManifest.xml, build.gradle.bak, temp_project template)
- Move README-only images out of app asset bundle to reduce APK/IPA size (~1.68MB)
- Fix logo filename typo (transparant -> transparent)
- Deduplicate _readPositiveInt into shared int_utils.dart
- Deduplicate _themeModeFromString (reuse from theme_settings.dart)
- Remove deprecated LocalLibraryState.items getter
- Remove unused sqflite_common_ffi dependency
- Update apps.json version to 4.5.1
- Fix Flutter version in CONTRIBUTING.md (3.38.1 -> 3.41.5)
- Improve .gitignore patterns (NUL, *.bak, root AndroidManifest.xml)

android/app/build.gradle.bak

@@ -1,71 +0,0 @@
-plugins {
-    id "com.android.application"
-    id "kotlin-android"
-    id "dev.flutter.flutter-gradle-plugin"
-}
-
-def localProperties = new Properties()
-def localPropertiesFile = rootProject.file('local.properties')
-if (localPropertiesFile.exists()) {
-    localPropertiesFile.withReader('UTF-8') { reader ->
-        localProperties.load(reader)
-    }
-}
-
-def flutterVersionCode = localProperties.getProperty('flutter.versionCode')
-if (flutterVersionCode == null) {
-    flutterVersionCode = '1'
-}
-
-def flutterVersionName = localProperties.getProperty('flutter.versionName')
-if (flutterVersionName == null) {
-    flutterVersionName = '1.0'
-}
-
-android {
-    namespace "com.zarz.spotiflac"
-    compileSdk flutter.compileSdkVersion
-    ndkVersion flutter.ndkVersion
-
-    compileOptions {
-        sourceCompatibility JavaVersion.VERSION_1_8
-        targetCompatibility JavaVersion.VERSION_1_8
-    }
-
-    kotlinOptions {
-        jvmTarget = '1.8'
-    }
-
-    sourceSets {
-        main.java.srcDirs += 'src/main/kotlin'
-    }
-
-    defaultConfig {
-        applicationId "com.zarz.spotiflac"
-        minSdkVersion flutter.minSdkVersion
-        targetSdk flutter.targetSdkVersion
-        versionCode flutterVersionCode.toInteger()
-        versionName flutterVersionName
-    }
-
-    buildTypes {
-        release {
-            signingConfig signingConfigs.debug
-            minifyEnabled false
-            shrinkResources false
-        }
-    }
-}
-
-flutter {
-    source '../..'
-}
-
-dependencies {
-    // Go backend library (gomobile generated)
-    implementation fileTree(dir: 'libs', include: ['*.aar'])
-    
-    // Kotlin coroutines for async Go backend calls
-    implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.7.3'
-    implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.7.3'
-}

android/app/src/main/kotlin/com/example/temp_project/MainActivity.kt

@@ -1,5 +0,0 @@
-package com.example.temp_project
-
-import io.flutter.embedding.android.FlutterActivity
-
-class MainActivity : FlutterActivity()