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/file_list.h

@@ -0,0 +1,35 @@
+#ifndef FILE_LIST_H
+#define FILE_LIST_H
+
+#include <stdbool.h>
+#include <stddef.h>
+
+/* --files-from allow-set. The file lists source paths RELATIVE to the source
+ * root. A listed regular file is transferred; a listed directory transfers its
+ * whole subtree (FastSync's recursion is always on). Blank lines are ignored.
+ *
+ * Entries are normalized: leading "./" and duplicate "/" are removed, an entry
+ * of "." means the whole tree, absolute entries and ".." traversal are
+ * rejected at parse time. The set is immutable and shared read-only across
+ * scanner worker threads.
+ */
+
+typedef struct {
+  char** entries; /* normalized rel paths; "" means the whole tree */
+  int count;
+} FileListSet;
+
+/* Load and validate a --files-from file. When `null_separated` (-0/--from0)
+ * entries are delimited by NUL instead of newlines. Returns NULL with a message
+ * in `err` on open/validation failure. An empty file yields an empty set
+ * (nothing is transferred). */
+FileListSet* file_list_load(const char* path, bool null_separated, char* err, size_t err_size);
+void file_list_destroy(FileListSet* set);
+
+/* True when `rel` (path relative to the source root, "" == root) is a listed
+ * entry, lives under a listed directory, or is an ancestor directory of a
+ * listed entry. Used to prune scanning: directories are descended only when
+ * this returns true, files are transferred only when it returns true. */
+bool file_list_affects(const FileListSet* set, const char* rel);
+
+#endif