refactor: extract receive_chunk_data and receive_manifest shared helpers

- receive_chunk_data(fd, config) -> Chunk*: shared receive/decompress/deserialize
  (eliminates ~25 lines of duplication between server.c and multiprocessing.c)
- receive_manifest(fd, config, next_status): moved from server.c to file.c,
  fixes missing 'Deleting files not in manifest...' log in multiprocessing.c
- Removes redundant manual free loop in multiprocessing.c manifest handling
  (array_list_create(free) destructor already handles this)
- server.c and multiprocessing.c: remove local chunk/manifest helpers,
  remove compression.h include (no longer needed)

src/shared/file.c

@@ -184,8 +184,7 @@ bool file_save_to_disk(const char *root_directory, File *file) {
   return ok;
 }
 
-File *receive_incremental_check(int fd, Config *config, bool *skipped) {
-  *skipped = false;
+File *receive_incremental_check(int fd, Config *config, bool *skipped) {  *skipped = false;
   char *check_path = receive_str(fd);
   if (check_path == NULL) { send_status(fd, STATUS_ERROR); return NULL; }
 
@@ -348,4 +347,21 @@ size_t file_content_to_buffer(File *file) {
   return bytes_read;
 }
 
+int receive_manifest(int fd, Config *config, int *next_status) {
+  int count;
+  if (!receive_int(fd, &count)) return -1;
+  ArrayList *manifest = array_list_create(free);
+  if (manifest) {
+    for (int i = 0; i < count; i++) {
+      char *s = receive_str(fd);
+      if (s) array_list_add(manifest, s);
+    }
+    fprintf(stderr, "Deleting files not in manifest...\n");
+    delete_extras(config->receive_root_directory, manifest);
+    array_list_delete(manifest);
+  }
+  if (!receive_status(fd, next_status)) return -1;
+  return 0;
+}
+