fix: tools/multimodal toggles now fallback to model capability
The getter functions for tools and multimodal overrides were defaulting
to `false` instead of falling back to the model's actual capability.
This caused stale user settings to override newer model capabilities.
For example, if a user visited a model before it gained tools support,
their settings stored `toolsOverrides[modelId] = false`. When the model
later added tools support, the toggle still showed OFF because it read
the stored `false` value instead of the model's `supportsTools: true`.
Now the getters correctly fall back to model capability, matching the
pattern already used in the sidebar layout and ChatWindow components.
