refactor: standardize doxygen briefs

Update the file-level \brief Doxygen tags across all 19 header and source
files in the src/ directory to ensure consistent, highly detailed, and
standardized documentation.

Author: fangfufu

src/fuse_local.h

@@ -26,7 +26,7 @@
 
 /**
  * \file fuse_local.h
- * \brief FUSE related functions
+ * \brief FUSE mounting and operations header
  */
 
 /* Initialise fuse */

src/link.h

@@ -26,7 +26,7 @@
 
 /**
  * \file link.h
- * \brief link related structures and functions
+ * \brief Link structure and handling functions header
  */
 
 #include <curl/curl.h>

src/network.h

@@ -26,7 +26,7 @@
 
 /**
  * \file network.h
- * \brief network related functions
+ * \brief Network transfer and cURL wrapper header
  */
 
 #include <curl/curl.h>

src/sonic.h

@@ -25,7 +25,7 @@
 #define SONIC_H
 /**
  * \file sonic.h
- * \brief Sonic related function
+ * \brief Airsonic / Subsonic server API integration header
  */
 
 typedef struct {

src/util.h

@@ -25,7 +25,7 @@
 #define UTIL_H
 /**
  * \file util.h
- * \brief utility functions
+ * \brief Utility functions and memory allocation wrappers header
  */
 
 #include <pthread.h>