feat(filter): receiver-side protect/risk engine for dest-only entries

- new bounded config-wire block (BLOCK_PROTECT_RULES) serializes the sender's
  compiled filter rules to the receiver (bounded count + 256 KiB patterns;
  strict action/sides validation)
- receiver evaluates protect/risk in the whole-tree extras walk and the
  per-directory delete plans, so a dest-only entry matching 'P' is kept like
  rsync; dry-run would-delete enumeration also honours it
- --filter flips to parity (115/11/31); per-dir merge receiver re-derivation
  remains the documented residual

tests/test_fuzz_smoke.c

@@ -18,10 +18,11 @@
 
 /* P8 config-frame tail: super_mode (4) + copy-as presence (4) + uid (4) + gid (4). */
 #define P8_TAIL_BYTES 16
-/* Bytes after the P8 tail: report_dest_info (4), report_stats (4, wire-stats
- * wave) and compression_algo (4, codec wave).  The P8 fields sit this many
- * bytes before the end of the frame. */
-#define POST_P8_TAIL_BYTES 12
+/* Bytes after the P8 tail: report_dest_info (4), report_stats (4),
+ * report_deletes (4, --info=del wave), compression_algo (4, codec wave) and the
+ * receiver delete-protection count (4, protocol 2.28.0).  The P8 fields sit
+ * this many bytes before the end of the frame. */
+#define POST_P8_TAIL_BYTES 20
 
 /* Smoke test for chunk_deserialize fuzz target */
 static void test_fuzz_chunk_deserialize() {