fix(android): don't letterbox against the configure placeholder

H264Decoder.outputSize() reported the 320x240 configure() placeholder
until the codec parsed the in-band SPS, so fitVideo sized the view to
1488x1116 (1.33 aspect) and the first rendered frame(s) of 2.4 content
were visibly squished before the real size corrected it ~40ms later.
Report no size until INFO_OUTPUT_FORMAT_CHANGED delivers the real one:
the first frame renders into the fullscreen surface and the correct
letterbox follows immediately. Validated live on the Fairphone 6 (the
placeholder 'video size' line is gone from logcat; 25/25 JVM tests).

android/app/src/main/kotlin/screen_cast/decode/H264Decoder.kt

@@ -18,6 +18,11 @@ class H264Decoder {
 
     private var codec: MediaCodec? = null
     private var configured = false
+    // True once the codec parsed the in-band SPS (INFO_OUTPUT_FORMAT_CHANGED).
+    // Before that, outputFormat still carries the configure() placeholder and
+    // must not drive layout — sizing the view to it squishes the first frame(s).
+    @Volatile
+    private var realFormatSeen = false
     @Volatile
     private var renderSurface: Surface? = null
 
@@ -57,6 +62,7 @@ class H264Decoder {
             throw e
         }
         configured = true
+        realFormatSeen = false
     }
 
     /** Points the decoder at a (possibly new) render surface. */
@@ -117,6 +123,7 @@ class H264Decoder {
                 }
                 index == MediaCodec.INFO_OUTPUT_FORMAT_CHANGED -> {
                     // The codec parsed the SPS size; outputFormat is ready.
+                    realFormatSeen = true
                     android.util.Log.i(
                         "H264Decoder", "output format: " +
                             c.outputFormat.getInteger(MediaFormat.KEY_WIDTH) +
@@ -141,10 +148,11 @@ class H264Decoder {
         }
     }
 
-    /** The decoded resolution once the first keyframe has configured the codec. */
+    /** The decoded resolution, once the first keyframe configured the codec. */
     @Synchronized
     fun outputSize(): Pair<Int, Int>? {
         val c = codec ?: return null
+        if (!realFormatSeen) return null // still the configure() placeholder
         return try {
             val format = c.outputFormat
             val width = format.getInteger(MediaFormat.KEY_WIDTH)