feat: add command queue and FIFO pipe for unified input handling

Co-authored-by: aider (deepseek/deepseek-reasoner) <aider@aider.chat>

src/command.h

@@ -0,0 +1,19 @@
+#ifndef COMMAND_H
+#define COMMAND_H
+
+typedef enum {
+    CMD_CYCLE,          // toggle record/stop for a channel
+    CMD_STOP,           // force to idle
+    // CMD_LOOP_TOGGLE not needed, CYCLE covers it
+    CMD_BIND_CHANNEL,   // bind a channel index (data = channel)
+    CMD_UNBIND,         // reset bind to channel 0
+    // ADD and REMOVE are still driven via atomics for now
+} cmd_type_t;
+
+typedef struct {
+    cmd_type_t type;
+    int        channel;   // which channel; -1 means "current/bound"
+    int        data;      // extra parameter (e.g. bind channel number)
+} command_t;
+
+#endif