feat(KB-171): propagate availableModels prop through dashboard component tree

- Update App.tsx to fetch and pass availableModels to Board
- Update Board component to accept and pass availableModels to Column
- Update Column component to receive availableModels prop
- Update ListView to handle availableModels prop
- Update Board test mock to include availableModels prop

packages/dashboard/app/components/__tests__/Board.test.tsx

@@ -10,7 +10,7 @@ const columnRenderCounts: Record<string, number> = {};
 
 // Mock child components so we only test Board's own rendering
 vi.mock("../Column", () => ({
-  Column: React.memo(({ column, tasks, onToggleCollapse }: { column: string; tasks: Task[]; onToggleCollapse?: () => void }) => {
+  Column: React.memo(({ column, tasks, onToggleCollapse, availableModels }: { column: string; tasks: Task[]; onToggleCollapse?: () => void; availableModels?: unknown }) => {
     columnRenderCounts[column] = (columnRenderCounts[column] ?? 0) + 1;
     return (
       <div data-testid={`column-${column}`} data-tasks={JSON.stringify(tasks)}>