Improve native macOS renderer layout, rotation, cover art, and audio stability - #505

Summary

• fix the native macOS renderer view hierarchy so mirrored video fills the window and stays centered through connect-time resizes, manual rotation, fullscreen toggles, and stream resets
• restore connect/fullscreen polish with an animated initial stream resize and distinct manual R / Shift+R rotation animation, while keeping protocol/device rotation immediate
• keep playback state and window chrome in sync by clearing stale paused state on reconnect and showing streaming/paused resolution plus source fps in the title bar
• rebuild cover-art textures when metadata changes so -ca audio sessions keep album art visible instead of falling back to the idle screen
• fix a native macOS VideoToolbox teardown race by serializing decoder create/destroy/decode access, preventing crashes during stream shutdown/reset
• fix native macOS audio-only handoff/reconnect issues by preserving the cover-art window on audio teardown and using osxaudiosink instead of autoaudiosink on macOS
• clear stale native macOS cover art after paused/disconnected audio sessions while keeping quick reconnects working, and harden the Metal cover-art draw path to avoid an MPS crash during cleanup
• refresh the idle screen layout, shortcut hints, and fullscreen scaling behavior for the native macOS renderer
• merge the latest upstream/master changes into native-macos-renderer, including the v1.74 mDNS/llhttp/core updates

Testing

• cd build && cmake --build .
• cmake -S . -B build-dnssd -DUSE_DNS_SD=1 -DUSE_NATIVE_MACOS_RENDERER=ON && cmake --build build-dnssd
• DYLD_FALLBACK_LIBRARY_PATH=/opt/homebrew/lib ./uxplay -d 1 -h265 -s 3840x2160 -fps 30 -vsync no -ca
• verified fresh connect/reconnect, pause/resume, title-bar updates, R, Shift+R, Cmd+0, fullscreen enter/exit, stream-start resize animation, and idle-screen resizing
• verified -ca cover-art metadata updates no longer drop back to the idle screen
• verified Spotify/ALAC audio-only playback after prior screen mirroring, with cover art intact, pause/teardown no longer breaking reconnect, and local audio output working via the macOS audio sink
• verified paused/disconnected Spotify cover-art sessions return to a clean ready state without leaving stale art behind, and no longer hit the native macOS Metal/MPS crash during cleanup
• verified both macOS service-discovery build variants compile and start cleanly: default internal mDNS and -DUSE_DNS_SD=1 Bonjour/dns_sd