refactor: standardize error reporting on the log module

- Add log_perror() helper (context + strerror(errno)) to the log module
- Replace all bare perror() calls with log_perror() so errors are routed
  through the unified logger (stderr sink + optional --log-file sink)
- Convert fprintf(stderr, "Error:/Warning: ...") in client code to
  log_message(); raw fprintf kept only for progress/stats output

src/shared/chunk.c

@@ -20,7 +20,7 @@
 Chunk* chunk_create(File** items, int element_count) {
   Chunk* chunk = (Chunk*)malloc(sizeof(Chunk));
   if (chunk == NULL) {
-    perror("ERROR: Could not allocate memory for chunk structure");
+    log_perror("ERROR: Could not allocate memory for chunk structure");
     return NULL;
   }
 
@@ -118,7 +118,7 @@ Chunk* chunk_deserialize(Data* data, bool use_metadata) {
 
     char* path = malloc(path_len + 1);
     if (path == NULL) {
-      perror("Could not allocate memory for file path");
+      log_perror("Could not allocate memory for file path");
       array_list_delete(files);
       return NULL;
     }
@@ -191,7 +191,7 @@ Chunk* chunk_deserialize(Data* data, bool use_metadata) {
 
     void* file_data = malloc(file_data_size > 0 ? file_data_size : 1);
     if (file_data == NULL) {
-      perror("Could not allocate memory for file data");
+      log_perror("Could not allocate memory for file data");
       file_destroy(file);
       array_list_delete(files);
       return NULL;