docs(replay): Add THIRD_PARTY_NOTICES entry for SimpleMp4FrameMuxer (#5586)

* docs(replay): Add THIRD_PARTY_NOTICES entry for SimpleMp4FrameMuxer

SimpleMp4FrameMuxer is adapted from the flutter_screen_recorder library
and carries a complete attribution header, but the corresponding entry
in THIRD_PARTY_NOTICES.md was never added. Warden's check-code-attribution
flags the missing entry as independently required regardless of header
completeness.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* docs(replay): Cover all adapted flutter_screen_recorder and Curtains files

SimpleFrameMuxer and SimpleVideoEncoder are adapted from the same
flutter_screen_recorder library as SimpleMp4FrameMuxer; fold all three
into one notice entry. Also extend the existing Square Curtains scope to
list io.sentry.android.replay.Windows, which is adapted from Curtains but
was not mentioned.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* fix(replay): Correct adapted-from URL in SimpleVideoEncoder header

The attribution header pointed at the upstream SimpleFrameMuxer.kt
instead of SimpleVideoEncoder.kt.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>