feat(web): add workspace management UI (M2 #12)

- Create workspace listing page at /settings/workspaces
  - List all user workspaces with role badges
  - Create new workspace functionality
  - Display member count per workspace

- Create workspace detail page at /settings/workspaces/[id]
  - Workspace settings (name, ID, created date)
  - Member management with role editing
  - Invite member functionality
  - Delete workspace (owner only)

- Add workspace components:
  - WorkspaceCard: Display workspace info with role badge
  - WorkspaceSettings: Edit workspace settings and delete
  - MemberList: Display and manage workspace members
  - InviteMember: Send invitations with role selection

- Add WorkspaceMemberWithUser type to shared package
- Follow existing app patterns for styling and structure
- Use mock data (ready for API integration)

apps/api/src/users/dto/index.ts

@@ -0,0 +1,2 @@
+export * from "./update-preferences.dto";
+export * from "./preferences-response.dto";

apps/api/src/users/dto/preferences-response.dto.ts

@@ -0,0 +1,12 @@
+/**
+ * Response DTO for user preferences
+ */
+export interface PreferencesResponseDto {
+  id: string;
+  userId: string;
+  theme: string;
+  locale: string;
+  timezone: string | null;
+  settings: Record<string, unknown>;
+  updatedAt: Date;
+}

apps/api/src/users/dto/update-preferences.dto.ts

@@ -0,0 +1,25 @@
+import { IsString, IsOptional, IsObject, IsIn } from "class-validator";
+
+/**
+ * DTO for updating user preferences
+ */
+export class UpdatePreferencesDto {
+  @IsOptional()
+  @IsString({ message: "theme must be a string" })
+  @IsIn(["light", "dark", "system"], {
+    message: "theme must be one of: light, dark, system",
+  })
+  theme?: string;
+
+  @IsOptional()
+  @IsString({ message: "locale must be a string" })
+  locale?: string;
+
+  @IsOptional()
+  @IsString({ message: "timezone must be a string" })
+  timezone?: string;
+
+  @IsOptional()
+  @IsObject({ message: "settings must be an object" })
+  settings?: Record<string, unknown>;
+}