fix: remove duplicate docstrings from public functions in .c files

Public function docstrings belong exclusively in .h headers per
coding convention. Only static helper functions and static variables
retain docstrings in .c files. Removed 413 duplicate docstrings
across 185 files (15 CBM + 15 C SDK projects). All 30 projects
rebuild with zero errors.

drivers/0x0d_timer/0x0d_timer.c

@@ -50,14 +50,6 @@ static bool _heartbeat_callback(void) {
     return true;
 }
 
-/**
- * @brief Application entry point for the repeating timer demo
- *
- * Starts a 1-second repeating timer whose callback prints a
- * heartbeat message over UART.
- *
- * @return int Does not return
- */
 int main(void) {
     stdio_init_all();
     timer_driver_start(1000, _heartbeat_callback);