fix: apply Android bitrate and frame rate settings

[hatemragab]

Summary

• apply explicit Android videoBitrate through Media3 VideoEncoderSettings
• lower Android output frame rate with FrameDropEffect without attempting to upsample
• preserve the existing H.264 profile/level request in the same encoder factory
• centralize and unit-test bitrate/frame-rate resolution

Compatibility

• no channel-schema or minimum-platform changes
• bitrate requests remain advisory because device encoders may apply fallback
• no Android hardware/device run was performed; validation is compile, lint, and unit-test based

Validation

• flutter analyze --no-pub
• flutter test --no-pub (97 tests)
• ./gradlew :v_video_compressor:testDebugUnitTest :v_video_compressor:lintDebug :app:assembleDebug --console=plain (21 native tests, lint, debug APK assembly)
• git diff --check

Fixes #26