iOS/macOS: set podspec version to 8.0.0 to match bundled FFmpeg

The CocoaPods spec version was stale (7.1.1 / 1.0.0), so Podfile.lock showed
an old FFmpeg version even though the bundled libraries are FFmpeg 8.0.
Addresses the version confusion in #123 and #136 (runtime is already 8.0).

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