test(parity): option-wave rsync differentials + docs (109/21/26)

- tests/integration/test_option_parity.py: bwlimit parse matrix + throttle
  rate, --info flist/name/nonreg/del(dry+real+itemize)/remove, real-setpriv
  --ignore-errors, rsync-daemon -M forwarding evidence, filter protect/risk
  destination-only divergence pin.
- RSYNC_COMPAT.md: tally 109/21/26; --bwlimit and --ignore-errors -> Parity,
  --filter and -M -> Divergent with differential rationale, --info residual
  narrowed to the categories with no client-observable event.
- HANDOFF/README: protocol 2.27.0, option-wave summary.

src/client/scanner.h

@@ -218,7 +218,7 @@ typedef struct {
   int completed;
   Chunk* initial_chunk;
   ProtocolSession* allocation_session;
-  FilterNode* root_filter_node; /* root .rsync-filter context (owned by ps) */
+  FilterNode* root_filter_node;  /* root .rsync-filter context (owned by ps) */
   const ScannerOptions* options; /* borrowed scan options (--info=nonreg output) */
 } ParallelScanner;