rsync flags: -a, -n, -p, --exclude, --delete

Feature changes across 15 files:

- -a/--archive: enables -c -m -M (no -s, which slows transfers)
- -n/--dry-run: scan + print without connecting or transferring
- -p <port>: custom SSH port (passed as -p to ssh via execvp)
- --exclude <pattern>: glob-based filename filtering in scanner
- --delete: sender collects file manifest; receiver deletes unlisted files

Protocol: added STATUS_MANIFEST, use_delete field in Config wire format.
New utilities: glob_match(), delete_extras() with recursive directory walk.
Scanner: accepts exclude patterns; skips matching entries.
SSH transport: switched from execlp to execvp for dynamic port arg.
Server + multiprocessing: handle STATUS_MANIFEST in both single and
multithreaded receive paths.

Builds clean, all 7 tests pass.

src/shared/multiprocessing.h

@@ -3,6 +3,7 @@
 
 #include <threads.h>
 
+#include "array_list.h"
 #include "config.h"
 #include "file.h"
 #include "queue.h"
@@ -19,6 +20,7 @@ typedef struct {
   cnd_t condition_not_full_loader;
   cnd_t condition_not_empty_loader;
   bool loader_done;
+  ArrayList *manifest;
 } PipelineContextSender;
 
 typedef struct PipelineContextReceiver {