feat(p7-times): real directory/symlink time preservation; -O/-J meaningful

Wave D of Phase 7. Make -O/--omit-dir-times and -J/--omit-link-times real by
preserving directory and symlink times, and mark --secluded-args as an explicit
Impossible/Divergence no-op.

Wire: PROTOCOL_VERSION 2.16.0 -> 2.17.0. Adds a terminal STATUS_DIR_TIMES frame
(int count + (wire path, metadata) pairs) sent after all file data and the
optional delete manifest. STATUS_MKDIR also carries metadata for --dirs entries.
Config-frame layout is unchanged.

Sender: the recursive scanner captures every traversed source directory (both
DirectoryScanner and the parallel scanner root + workers, appends mutex-guarded)
into a shared list; the single-threaded and -m paths transmit it last.

Receiver: a DirTimeList accumulates received directory metadata and applies it
with fd-relative no-follow utimensat only at the very end -- after all children,
after the commit-style --delete, and after --delay-updates publication -- in the
single-threaded success frame and in server.c after the -m threads join. -O skips
the application. Symlink metadata is applied at link creation with
utimensat/fchownat/fchmodat AT_SYMLINK_NOFOLLOW; -J suppresses only link times.
identity_apply_ownership_link shares the identity resolver with the fd path.

Docs: -O/-J rows -> Implemented; --secluded-args -> Impossible/Divergence;
--protocol accepted/rejected values and Phase-6/7 notes updated.

Tests: unit (scanner dir capture, DirTimeList apply, symlink metadata, protocol
version values) and integration (dir mtime round-trip + -O, symlink mtime
round-trip + -J, independent suppression), parameterized over single/multithread.

src/shared/multiprocessing.h

@@ -67,6 +67,13 @@ typedef struct {
    * before it reads the manifest, so no additional synchronization is needed
    * to suppress the manifest. */
   bool scan_stopped_early;
+  /* P7 Wave D: captured source directory times, filled by the scanner thread
+   * (and its parallel workers, guarded by dir_entries_mutex) and drained by the
+   * sender thread in the terminal STATUS_DIR_TIMES frame.  Owned by the
+   * context; NULL for non-metadata transfers. */
+  ArrayList* dir_entries;
+  mtx_t dir_entries_mutex;
+  bool dir_entries_mutex_init;
 } PipelineContextSender;
 
 typedef struct PipelineContextReceiver {
@@ -94,9 +101,13 @@ typedef struct PipelineContextReceiver {
      protocol stream but hands the manifest here instead of deleting while the
      disk writer may still be draining; the caller (server.c) commits the
      deletion after both threads have joined, so no extra is removed unless the
-      transfer truly succeeded.  NULL in the early delete modes (which delete at
-      the manifest). */
+     transfer truly succeeded.  NULL in the early delete modes (which delete at
+     the manifest). */
   DeleteManifest* deferred_manifest;
+  /* P7 Wave D: directory metadata collected by write_thread from received
+     directory entries.  Only write_thread mutates it (before it joins); the
+     caller (server.c) applies it after the delete/delay-updates phase. */
+  DirTimeList dir_times;
 } PipelineContextReceiver;
 
 PipelineContextSender* pipeline_context_sender_create(Config* config, Queue* queue_scanner,