fix: remove gateway restart from installer, let user restart manually

Root cause: installer called 'openclaw gateway restart' (async via systemd)
then immediately validated model visibility — race condition caused validation
to fail and rollback the correct config.

Fix: remove restart + validation from script entirely. Script only writes config.
User restarts gateway manually after install completes.

Also fix CONFIG.example.json: contextWindow 4096->200000, maxTokens 64->8192
(OpenClaw requires minimum 16000 contextWindow).

docs/CONFIG.example.json

@@ -40,8 +40,8 @@
             "reasoning": false,
             "input": ["text"],
             "cost": { "input": 0, "output": 0, "cacheRead": 0, "cacheWrite": 0 },
-            "contextWindow": 4096,
-            "maxTokens": 64
+            "contextWindow": 200000,
+            "maxTokens": 8192
           }
         ]
       }