feat: add domains, ideas, layouts, widgets API modules

- Add DomainsModule with full CRUD, search, and activity logging
- Add IdeasModule with quick capture endpoint
- Add LayoutsModule for user dashboard layouts
- Add WidgetsModule for widget definitions (read-only)
- Update ActivityService with domain/idea logging methods
- Register all new modules in AppModule

apps/web/src/components/widgets/widget-registry.ts

@@ -0,0 +1,22 @@
+/**
+ * Widget component registry - React-specific definitions
+ */
+
+import type { ComponentType } from "react";
+import type { WidgetProps } from "@mosaic/shared";
+
+/**
+ * Widget component registry
+ */
+export interface WidgetComponent {
+  name: string;
+  displayName: string;
+  description: string;
+  component: ComponentType<WidgetProps>;
+  defaultWidth: number;
+  defaultHeight: number;
+  minWidth: number;
+  minHeight: number;
+  maxWidth?: number;
+  maxHeight?: number;
+}