fix(ws): friendlier error when Gateway kernel does not support v3 handshake (#272)

- Detect 'device signature invalid' / 'protocol mismatch' on WebSocket close (code 1008)
- Detect DEVICE_AUTH_SIGNATURE_INVALID/PROTOCOL_VERSION_MISMATCH on connect failure after auto-pair
- Replace cryptic English reason with kernel.tooOldForProtocol message (zh-CN + en)
- Suggest upgrading Gateway kernel to recommended version (2026.5.x)
- Stop auto-reconnect loop in these unrecoverable cases

src/locales/en.json

@@ -2237,7 +2237,8 @@
       "title": "New kernel available",
       "subtitle": "{from} → {to}, click to upgrade",
       "dismissTooltip": "Don't remind me this session"
-    }
+    },
+    "tooOldForProtocol": "Gateway kernel is too old and does not support the handshake protocol used by this ClawPanel. Please upgrade the OpenClaw kernel to the recommended version ({recommended}) and retry. You can upgrade from \"Services → OpenClaw → Upgrade\"."
   },
   "cliConflict": {
     "title": "Detected {count} possibly conflicting OpenClaw installation(s)",