Address re-review: AAC re-encode, probe fallthrough, HDR detection

- Android non-AAC audio is now transcoded to AAC (matching iOS) via a
  source-decoder -> AAC-encoder pre-pass that captures the encoder's
  output format before the muxer starts, then writes buffered samples
  after the video pipeline finishes. Falls back to dropping audio if
  the transcode fails.
- compress.ts wraps probe() in try/catch and falls through to
  passthrough on failure instead of throwing.
- Probers expose isHDR (HLG/PQ via color transfer, plus Dolby Vision
  codecs/mimes); shouldCompress forces compression for HDR sources so
  the SDR BT.709 path always runs. Also sets
  KEY_COLOR_TRANSFER_REQUEST=SDR on the Android decoder (API 31+) so
  HDR sources tone-map to SDR pixels instead of being mislabeled.

modules/expo-bluesky-video-compress/ios/VideoProber.swift

@@ -23,8 +23,24 @@ struct VideoProber {
     let formatDescriptions = try await videoTrack.load(.formatDescriptions)
 
     var codec = "unknown"
+    var isHDR = false
     if let formatDescription = formatDescriptions.first {
-      codec = fourCCToString(CMFormatDescriptionGetMediaSubType(formatDescription))
+      let subType = CMFormatDescriptionGetMediaSubType(formatDescription)
+      codec = fourCCToString(subType)
+      // Dolby Vision codecs are HDR by definition.
+      let dolbyVisionSubtypes: Set<String> = ["dvhe", "dvh1", "dvav", "dva1"]
+      if dolbyVisionSubtypes.contains(codec) {
+        isHDR = true
+      } else if let extensions = CMFormatDescriptionGetExtensions(formatDescription)
+        as? [String: Any]
+      {
+        let transferKey = kCMFormatDescriptionExtension_TransferFunction as String
+        if let transfer = extensions[transferKey] as? String {
+          let hlg = kCMFormatDescriptionTransferFunction_ITU_R_2100_HLG as String
+          let pq = kCMFormatDescriptionTransferFunction_SMPTE_ST_2084_PQ as String
+          isHDR = transfer == hlg || transfer == pq
+        }
+      }
     }
 
     let rotation = rotationFromTransform(preferredTransform)
@@ -66,7 +82,8 @@ struct VideoProber {
       "codec": codec,
       "hasAudio": hasAudio,
       "frameRate": nominalFrameRate,
-      "rotation": rotation
+      "rotation": rotation,
+      "isHDR": isHDR
     ]
   }