Fix C64 display rendering and keyboard matrix

- Remove android:background from C64DisplayView: SurfaceView's XML
    background painted over the surface, hiding all rendered content
  - Fix pixel byte order: copyPixelsFromBuffer reads [R,G,B,A] bytes, so
    physical colors must be packed as ABGR (not ARGB) to avoid R/B swap
  - Fix six wrong C64 keyboard matrix positions (1, 2, Q, E, R, Y) taken
    from the authoritative VICE hardware matrix table

SchwertUndMagieOnPebbleCompanionApp/gradle/libs.versions.toml

@@ -1,6 +1,7 @@
 [versions]
 agp = "9.2.1"
 coreKtx = "1.10.1"
+documentfile = "1.0.1"
 junit = "4.13.2"
 junitVersion = "1.1.5"
 espressoCore = "3.5.1"
@@ -20,6 +21,7 @@ material = { group = "com.google.android.material", name = "material", version.r
 androidx-activity-ktx = { group = "androidx.activity", name = "activity-ktx", version.ref = "activityKtx" }
 androidx-constraintlayout = { group = "androidx.constraintlayout", name = "constraintlayout", version.ref = "constraintlayout" }
 nanohttpd = { group = "org.nanohttpd", name = "nanohttpd", version.ref = "nanohttpd" }
+androidx-documentfile = { group = "androidx.documentfile", name = "documentfile", version.ref = "documentfile" }
 
 [plugins]
 android-application = { id = "com.android.application", version.ref = "agp" }