fix: enforce strictly subtractive toolset filtration

Refactor tool resolution logic in model_tools.py to ensure that
disabled_toolsets are always subtracted at the end, preventing
composite toolsets (e.g. 'browser') from implicitly enabling tools
that should be hidden.

- Added 'disabled_toolsets' to DEFAULT_CONFIG in hermes_cli/config.py
- Updated HermesCLI in cli.py to load and propagate disabled toolsets to AIAgent
- Implemented robust two-phase resolution (additive then subtractive) in model_tools.py

hermes_cli/config.py

@@ -457,6 +457,7 @@ DEFAULT_CONFIG = {
         # remains available as a tool regardless of this setting — the routing
         # only controls how inbound user images are presented.
         "image_input_mode": "auto",
+        "disabled_toolsets": [],
     },
     
     "terminal": {