devices: --devices/--specials/-D/--copy-devices/--write-devices

Recreate char/block nodes via mknodat (privilege-gated, EPERM->warn+skip) and
FIFOs via mkfifoat; new STATUS_SPECIAL frame + validated rdev; sockets skipped;
-copy-devices copies st_size; -write-devices O_NOFOLLOW+O_NONBLOCK warn+skip.
preserve_specials/copy_devices/write_devices cross the wire. PROTOCOL_VERSION
2.12.0->2.13.0. Review fixes: -m source-removal keeps recreated specials, FIFO
ENXIO skip, rdev bounds at chunk_deserialize, STATUS_ERROR on receive branch,
scanner_prepare_special dedup.

src/shared/multiprocessing.c

@@ -308,8 +308,9 @@ int write_thread(void* pipeline_context) {
     }
     /* Record the per-file outcome so a --remove-source-files sender learns
        which sources were actually written versus skipped on the receiver.
-       Explicit directory entries have no source and are never acknowledged. */
-    if (context->config->remove_source_files && !file->is_dir && !file->skip &&
+       Explicit directory entries and recreated device/special nodes have no
+       source and are never acknowledged (mirrors receiver.c). */
+    if (context->config->remove_source_files && !file->is_dir && !file->is_special && !file->skip &&
         !receiver_outcomes_append(&context->outcomes, (unsigned char)result)) {
       file_destroy(file);
       pipeline_context_receiver_note_bytes_released(context, file_bytes);