feat: add --files-from/-0, --filter, -C and -F filter layer

Implement the RSYNC_COMPAT Phase-2 filter/parser feature group:
- --files-from=FILE (repeatable) plus -0/--from0 NUL delimiters: parse the
  source file list relative to the source root into a shared read-only
  allow-set; the scanner transfers listed files and the whole subtree of
  listed directories and prunes everything else in single- and
  multithreaded mode. Absolute/'..' entries and missing files are hard
  CLI errors.
- --filter=RULE: rsync-style +/- rules (anchored '/', dir-only trailing '/',
  word include/exclude forms) evaluated first-match-wins with a default of
  include, as an independent layer from legacy --exclude/--include.
  Unsupported directives (merge/hide/... ) are rejected explicitly. -f stays
  sendfile.
- -C/--cvs-exclude: well-known rsync CVS default exclude set.
- -F: per-directory .rsync-filter files read during traversal and applied to
  the owning directory's subtree (single + parallel), never transferred.
- Delete manifest still derives from what was actually sent.

Client-only config fields; no wire/protocol change. Adds unit coverage
(CLI parse, allow-set and filter scanning single+parallel) and integration
tests (TestFilesFrom, TestFilters). RSYNC_COMPAT matrix rows updated:
5 rows move to Implemented (Summary 62/3/5/1/76 = 147).

src/shared/config.h

@@ -100,10 +100,14 @@ typedef struct Config {
   bool delete_after;
   int max_delete;
 
-  // Issue #129: Advanced file selection
-  ArrayList* filters;
-  char* files_from;
-  bool cvs_exclude;
+  // Issue #129: Advanced file selection. These fields are CLIENT-ONLY: they are
+  // never serialized to the wire (the receiver must not learn them).
+  ArrayList* filters;   /* --filter=RULE rule strings, in order */
+  char* files_from;     /* --files-from path (may be NULL) */
+  void* files_from_set; /* parsed FileListSet* allow-set, or NULL */
+  bool from0;           /* -0/--from0: NUL-delimited *-from files */
+  bool cvs_exclude;     /* -C/--cvs-exclude: standard CVS ignore set */
+  bool per_dir_filter;  /* -F: apply per-directory .rsync-filter files */
   bool prune_empty_dirs;
   bool one_file_system; /* -x/--one-file-system: do not cross filesystem boundaries */
   bool relative;