feat: multiple test patterns in testpattern node

V210.hpp: add fill_colorbars, fill_ire_ramp, fill_black, fill_white.
Shared fill_solid helper stamps the first line across all rows via
memcpy. Generic write_palette_line template handles both SMPTE and
IRE bar palettes. fill_frame kept as a backward-compat alias.

testpattern/main.cpp: read "pattern" from node config and dispatch
to the appropriate fill function (bars/ire/black/white).

build_graph: pass {"pattern","bars"} to testpattern node params.

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

studio-manager/main.cpp

@@ -41,9 +41,10 @@ static dmf::FlowGraph build_graph() {
     const std::string video_flow = gen_uuid();
     const std::string audio_flow = gen_uuid();
     g.nodes = {
-        { "ndiin",    "ndiin",    {} },
-        { "fakesink", "fakesink", {} },
-        { "ndiout",   "ndiout",   {} },
+        { "testpattern", "testpattern", {{"pattern", "bars"}} },
+        { "ndiin",       "ndiin",       {} },
+        { "fakesink",    "fakesink",    {} },
+        { "ndiout",      "ndiout",      {} },
     };
     const nlohmann::json video_fmt = {
         {"kind","video"}, {"width",1920}, {"height",1080}, {"fps_num",25}, {"fps_den",1}