add header doc comments to non-obvious util data structures

debug_log/ring_buffer.h

@@ -3,6 +3,9 @@
 #include <cstdint>
 #include <span>
 
+// Fixed-capacity FIFO with wrap-around. push_overwrite drops the oldest entry
+// when full -- used by the debug log so dlog never blocks or fails. Iteration
+// walks logical positions head..tail, hiding the modular indexing.
 template <typename T, uint16_t N>
 struct ring_buffer {
     std::array<T, N> data = {};