Add OBS RTMP interoperability gate

[anvsk]

What changed

• add reproducible OBS RTMP publisher and consumer scenarios to tools/interop.ps1
• validate publisher output with ffprobe packet, keyframe and monotonic timestamp checks
• validate consumer output by decoding the OBS PNG screenshot and checking pixel diversity
• separate OBS and VLC desktop preconditions, pin MediaMTX, and report RTMP state/tool versions
• update the roadmap, support matrix, RTMP report and pause handoff while keeping RTMP experimental

Why

V3-03F2 required evidence that OBS can both publish into aimedia and render aimedia's RTMP output. Connection state alone was insufficient: the gate now proves media packets and an actual non-blank rendered frame.

Root causes fixed while building the gate

• OBS-only suites were coupled to the VLC SRT plugin preflight.
• the RTMP source could start before aimedia's listener was ready.
• the previous rendered-frame check used PNG byte size, which rejected a valid, highly compressed SMPTE-bars frame.

Validation

• rtmp-obs suite passed with OBS 30.0.2.1 and MediaMTX 1.20.0
  • publisher: H.264/AAC, 581/948 packets, first video keyframe, monotonic PTS/DTS
  • consumer: H.264 1280x720, AAC 48kHz stereo, 13 decoded colors
• existing SRT obs suite passed: 300/469 packets and 16 decoded colors
• PowerShell syntax and Python AST checks passed
• runtime image contains no ffmpeg, ffprobe, or libav libraries
• git diff --check passed

Product status

RTMP/RTMPS remains experimental. Real domestic/overseas platform endpoints and the full two-hour GPU soak remain open as V3-03F3/F4.