feat: fan-out ndiin video flow to both fakesink and ndiout

Share a single UUID across both edges so both readers connect to the
same MXL flow. MXL supports multiple readers per flow natively — each
reader has its own read pointer into the ring buffer.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

studio-manager/main.cpp

@@ -38,12 +38,16 @@ static std::string gen_uuid() {
 
 static dmf::FlowGraph build_graph() {
     dmf::FlowGraph g;
+    const std::string video_flow = gen_uuid();
     g.nodes = {
         { "ndiin",    "ndiin",    {} },
         { "fakesink", "fakesink", {} },
+        { "ndiout",   "ndiout",   {} },
     };
     g.edges = {
-        { gen_uuid(), "ndiin", "flow_id", "fakesink", "flow_id",
+        { video_flow, "ndiin", "flow_id", "fakesink", "flow_id",
+          { {"kind","video"}, {"width",1920}, {"height",1080}, {"fps_num",25}, {"fps_den",1} } },
+        { video_flow, "ndiin", "flow_id", "ndiout",   "flow_id",
           { {"kind","video"}, {"width",1920}, {"height",1080}, {"fps_num",25}, {"fps_den",1} } },
     };
     return g;