Linker errors on Windows fixed; zero-playout-delay video mode added

Fixes

• Fix PeerContext forward-declaration in jsep.h from class to struct to match the cxx bridge definition, resolving LNK2019 linker errors on windows-msvc - #1154
• Add an opt-in zero-playout-delay mode for native video subscribers, expose it through the local_video subscriber's --low-latency flag, and isolate subscriber diagnostics from frame-driven video rendering.