Adds a Settings gear button to the InsightsView action bar that toggles a
collapsible model configuration row. The row contains a CustomModelDropdown
allowing users to override the insight generation model. Selections persist
to localStorage under the "fusion-insight-model" key. A yellow indicator dot
appears on the gear when a non-default model is active.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
