chore: remove dead top-level toolsets config key

The top-level 'toolsets' key in config.yaml was never read at runtime.
Tool selection uses platform_toolsets (per-platform) or the --toolsets
CLI flag. The key existed in load_cli_config() defaults and the example
config as 'toolsets: [all]', misleading users into thinking it
controlled tool availability.

- Remove from load_cli_config() hardcoded defaults
- Remove from hermes config show output
- Replace in cli-config.yaml.example with deprecation note pointing
  to platform_toolsets and hermes tools

hermes_cli/config.py

@@ -1607,7 +1607,6 @@ def show_config():
     print(color("◆ Model", Colors.CYAN, Colors.BOLD))
     print(f"  Model:        {config.get('model', 'not set')}")
     print(f"  Max turns:    {config.get('agent', {}).get('max_turns', DEFAULT_CONFIG['agent']['max_turns'])}")
-    print(f"  Toolsets:     {', '.join(config.get('toolsets', ['all']))}")
     
     # Display
     print()