fix: correct atomic pointer declaration syntax

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

src/looper.c

@@ -13,7 +13,7 @@
 #include <string.h>
 
 /* Global state (shared across files) */
-_Atomic struct channel_t *channels = NULL;
+struct channel_t *_Atomic channels = NULL;
 atomic_int channel_capacity = 0;
 atomic_int channel_count = 0;
 int next_channel_id = 1;