fix: Remove dynamic build date for Reproducible Builds

Fixes #7 - Thanks @IzzySoft for reporting and investigating!

Removed:
- getBuildDate() function from build.gradle.kts
- BUILD_DATE buildConfigField
- Build date display in SettingsActivity

Sorry for the hour of work this caused - will be more careful about RB in the future.

android/app/build.gradle.kts

@@ -24,9 +24,6 @@ android {
         versionName = "1.4.0"  // 🚀 v1.4.0: Checklists, Multi-Device Sync Fixes, UX Improvements
 
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
-        
-        // 🔥 NEU: Build Date für About Screen
-        buildConfigField("String", "BUILD_DATE", "\"${getBuildDate()}\"")
     }
     
     // Disable Google dependency metadata for F-Droid/IzzyOnDroid compatibility
@@ -144,12 +141,6 @@ dependencies {
     androidTestImplementation(libs.androidx.espresso.core)
 }
 
-// 🔥 NEU: Helper function für Build Date
-fun getBuildDate(): String {
-    val dateFormat = SimpleDateFormat("yyyy-MM-dd", Locale.US)
-    return dateFormat.format(Date())
-}
-
 // ⚡ v1.3.1: ktlint deaktiviert wegen Parser-Problemen
 // Aktivieren in v1.4.0 wenn Code-Stil bereinigt wurde
 // ktlint {