Fix iOS silent audio-only output and Android Dolby Vision .MOV failures

[Copilot]

Two video regressions: on iOS (since numandev1#392) Video.compress could resolve successfully with an MP4 containing only audio — the video track was silently dropped; on Android, iPhone Dolby Vision .MOV inputs failed hard with Failed to initialize video/dolby-vision, error 0xfffffffe (NAME_NOT_FOUND).

iOS — audio-only result (VideoMain.swift)

• Removed AVVideoExpectedSourceFrameRateKey and AVVideoAverageNonDroppableFrameRateKey from the H.264 compressionDict. These aren't documented avc1 compression properties: AVAssetWriter.canApply(...) returns true, but the iOS encoder drops the video track while the export still ends as .completed.
• Added a post-export guard that rejects results whose output asset has no video track, instead of returning an audio-only file as success.

let outputAsset = AVAsset(url: outputURL)
if outputAsset.tracks(withMediaType: .video).isEmpty {
  try? FileManager.default.removeItem(at: outputURL)
  onFailure(CompressionError(message: "Compression produced a file with no video track"))
} else {
  onCompletion(outputURL)
}

Android — Dolby Vision .MOV (CompressorUtils.kt, Compressor.kt)

• The decoder is created from the input track MIME; video/dolby-vision has no decoder on most devices. New ensureDecodableVideoFormat(...) runs before createDecoderByType and, when the dedicated decoder is missing, remaps to the backward-compatible base layer (profiles 8.x/4 → HEVC, 9 → AVC; unknown → HEVC, the common iPhone case).
• Non-backward-compatible profiles (5/7) now surface a clear error rather than a cryptic native crash.

Docs

• TRIAGE.md: added rows + fix entries for both issues.
• CLAUDE.md (new): repo layout, build/test commands, and native-pipeline pitfalls — including both failure modes above.

Notes

The native paths are verified by review only; per the repo's testing model the JS tests mock the native module, so real decode/encode should be smoke-tested in the example app on a simulator/device.