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/utils.h

@@ -1,8 +1,13 @@
 #ifndef UTILS_H
 #define UTILS_H
 
+#include "array_list.h"
+#include <stdbool.h>
+
 void mkdir_r(char *path);
 char *str_dup(const char *string);
 char *path_cat(char *path1, char *path2);
+bool glob_match(const char *pattern, const char *str);
+void delete_extras(const char *dest_root, ArrayList *manifest);
 
 #endif