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/api/src/domains/dto/update-domain.dto.ts

@@ -0,0 +1,50 @@
+import {
+  IsString,
+  IsOptional,
+  MinLength,
+  MaxLength,
+  Matches,
+  IsObject,
+} from "class-validator";
+
+/**
+ * DTO for updating an existing domain
+ * All fields are optional to support partial updates
+ */
+export class UpdateDomainDto {
+  @IsOptional()
+  @IsString({ message: "name must be a string" })
+  @MinLength(1, { message: "name must not be empty" })
+  @MaxLength(255, { message: "name must not exceed 255 characters" })
+  name?: string;
+
+  @IsOptional()
+  @IsString({ message: "slug must be a string" })
+  @MinLength(1, { message: "slug must not be empty" })
+  @MaxLength(100, { message: "slug must not exceed 100 characters" })
+  @Matches(/^[a-z0-9-]+$/, {
+    message: "slug must contain only lowercase letters, numbers, and hyphens",
+  })
+  slug?: string;
+
+  @IsOptional()
+  @IsString({ message: "description must be a string" })
+  @MaxLength(10000, { message: "description must not exceed 10000 characters" })
+  description?: string | null;
+
+  @IsOptional()
+  @IsString({ message: "color must be a string" })
+  @Matches(/^#[0-9A-F]{6}$/i, {
+    message: "color must be a valid hex color code (e.g., #FF5733)",
+  })
+  color?: string | null;
+
+  @IsOptional()
+  @IsString({ message: "icon must be a string" })
+  @MaxLength(50, { message: "icon must not exceed 50 characters" })
+  icon?: string | null;
+
+  @IsOptional()
+  @IsObject({ message: "metadata must be an object" })
+  metadata?: Record<string, unknown>;
+}