Disallow WebFetch tool for non-Anthropic providers

WebFetch, like WebSearch, is an Anthropic-only tool. Add it to the
disallowed tools list when the provider is not Anthropic.

Author: Mng-dev-ai

backend/app/services/claude_agent.py

@@ -539,10 +539,11 @@ async def _build_claude_options(
             for env_var in user_settings.custom_env_vars:
                 env[env_var["key"]] = env_var["value"]
 
-        # WebSearch is an Anthropic-only tool — non-Anthropic providers don't support it
+        # WebSearch and WebFetch are Anthropic-only tools — non-Anthropic providers don't support them
         disallowed_tools: list[str] = []
         if provider_type != ProviderType.ANTHROPIC.value:
             disallowed_tools.append("WebSearch")
+            disallowed_tools.append("WebFetch")
 
         sdk_permission_mode = SDK_PERMISSION_MODE_MAP.get(
             permission_mode, "acceptEdits"