refactor: DeckLinkReceiver readability and error handling

DeckLinkReceiver:
- Group private members with section comments (SDK objects / sync / frame state)
- Change wait_for_format timeout param from uint64_t to int (matches
  std::chrono::milliseconds and all call sites)

decklinkin main.cpp:
- Wrap start_capture in try/catch — logs error and returns cleanly on
  device init failure (consistent with NDIInNode pattern)
- Remove redundant zero-init on frame_buf (vector<uint8_t> zero-inits anyway)

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

nodes/decklinkin/main.cpp

@@ -8,15 +8,19 @@
 
 class DeckLinkInNode : public dmf::NodeBase {
     void run() override {
-        dmf::DeckLinkReceiver receiver;
-
-        log("Available DeckLink devices:");
-        for (const auto& d : receiver.devices)
-            log("  %u) %s", d.index, d.name.c_str());
-
         const uint32_t device_index = config().value("device_index", 0u);
-        receiver.start_capture(device_index);
-        log("Capturing from: %s", receiver.devices[device_index].name.c_str());
+
+        dmf::DeckLinkReceiver receiver;
+        try {
+            log("Available DeckLink devices:");
+            for (const auto& d : receiver.devices)
+                log("  %u) %s", d.index, d.name.c_str());
+            receiver.start_capture(device_index);
+            log("Capturing from: %s", receiver.devices[device_index].name.c_str());
+        } catch (const std::runtime_error& e) {
+            log("DeckLink init error: %s", e.what());
+            return;
+        }
 
         if (!receiver.wait_for_format(5000)) {
             log("Timeout waiting for format detection");
@@ -55,7 +59,7 @@ class DeckLinkInNode : public dmf::NodeBase {
         uint64_t          video_index = mxlGetCurrentIndex(&video_rate);
         log("start video_index=%llu", video_index);
 
-        std::vector<uint8_t> frame_buf(static_cast<size_t>(video_stride) * static_cast<size_t>(height), 0);
+        std::vector<uint8_t> frame_buf(static_cast<size_t>(video_stride) * static_cast<size_t>(height));
 
         while (dmf::g_running.load(std::memory_order_relaxed)) {
             if (!receiver.wait_for_frame(frame_buf.data(), video_stride, width, height)) break;