Fix Gemini CLI configuration file name: config.json -> settings.json

The correct configuration file for Gemini CLI is settings.json, not config.json.
This applies to both global (~/.gemini/settings.json) and project-specific
(.gemini/settings.json) configurations as confirmed by official documentation.

Author: ipapapa

docs/installation-guides/install-gemini-cli.md

@@ -124,8 +124,8 @@ Then configure:
 
 Gemini CLI uses a settings JSON file to configure MCP servers:
 
-- **Global configuration**: `~/.gemini/config.json`
-- **Project-specific**: `.gemini/config.json` in your project directory
+- **Global configuration**: `~/.gemini/settings.json`
+- **Project-specific**: `.gemini/settings.json` in your project directory
 
 ### Setup Steps