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/protocol.h

@@ -5,7 +5,7 @@
 #include <stddef.h>
 
 typedef int Status;
-enum NET_STATUS { STATUS_OK, STATUS_ERROR, STATUS_FINISHED, STATUS_NEXT, STATUS_CHUNK };
+enum NET_STATUS { STATUS_OK, STATUS_ERROR, STATUS_FINISHED, STATUS_NEXT, STATUS_CHUNK, STATUS_MANIFEST };
 
 void io_set_fds(int read_fd, int write_fd);
 void send_n_data(int file_descriptor, void *data, size_t data_size);