v1.3.1 — Screenshot capture fix & async capture_frames

What's New

• Fix: get_game_screenshot / capture_frames now read directly from the Game View's internal RenderTexture via reflection, eliminating editor chrome and tiling artifacts that crept in when the ScreenCapture.CaptureScreenshotAsTexture() timing was off
• Rework: capture_frames is now async — it returns a capture_id immediately, and the new get_captured_frames tool retrieves frames (including partial progress for long captures)
• Graceful fallback to camera-render when the Game View isn't available (edit mode, etc.)
• Session auto-purge (60s TTL) skips in-flight captures, so long runs aren't evicted mid-flight

Thanks to @Sandersm90 for the contribution!