docs: correct rsync-parity claims and stale facts (#297)

Reclassify every rsync-compatibility row as parity / caveat / divergent
(replacing the misleading 143-OK / 0-divergence summary), and document the
protocol 2.23.0 behavior:

- Split the conflated `-M, --preserve` row: `-M` is `--remote-option`,
  `--preserve` is the FastSync `-p`+`-t` alias.
- Fix `MAX_CONNECTION_MEMORY` (256 MiB, not 1 GB), `--rsync-path`
  (client-only, never crosses the wire), and the `-p` mode behavior
  (strict rsync parity; no masking).
- `--specials` now recreates sockets, so `-D` is real parity; fake-super
  records the resolved owner and replays mode/time (never real-chowns).
- Document short options/clustering, checksum/compression choices, seed
  randomization, timeout/max-alloc defaults, temp-dir confinement + EXDEV,
  identity/map parity, verbatim symlinks, delete scoping, `--max-delete`
  partial + exit 25, `--chmod`, output caveats, and server `--port`.
- Bump version refs to 2.23.0 and add the 2.23.0 CHANGELOG entry.

Docs-only; no source changes.

.opencode/skills/release/SKILL.md

@@ -16,7 +16,7 @@ Ask the user or determine from context:
 - **Minor** (x.Y.0) — new features, backward compatible
 - **Patch** (x.y.Z) — bug fixes, no protocol changes
 
-Current version: `PROTOCOL_VERSION "2.22.0"` in `src/shared/config.h`
+Current version: `PROTOCOL_VERSION "2.23.0"` in `src/shared/config.h`
 
 ### Step 2: Check Protocol Version