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/prisma/migrations/20260129225813_add_user_preferences/migration.sql

@@ -0,0 +1,18 @@
+-- CreateTable
+CREATE TABLE "user_preferences" (
+    "id" UUID NOT NULL,
+    "user_id" UUID NOT NULL,
+    "theme" TEXT NOT NULL DEFAULT 'system',
+    "locale" TEXT NOT NULL DEFAULT 'en',
+    "timezone" TEXT,
+    "settings" JSONB NOT NULL DEFAULT '{}',
+    "updated_at" TIMESTAMPTZ NOT NULL,
+
+    CONSTRAINT "user_preferences_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE UNIQUE INDEX "user_preferences_user_id_key" ON "user_preferences"("user_id");
+
+-- AddForeignKey
+ALTER TABLE "user_preferences" ADD CONSTRAINT "user_preferences_user_id_fkey" FOREIGN KEY ("user_id") REFERENCES "users"("id") ON DELETE CASCADE ON UPDATE CASCADE;