feat(01-04): add onboarding wizard with settings API and persisted state

- Settings API: GET/PUT /api/settings/:key with SQLite persistence
- useSettings hook with TanStack Query for settings CRUD
- OnboardingWizard: 3-step modal overlay (welcome, create category, add item)
- Root layout checks onboarding completion flag before rendering wizard
- Skip option available at every step, all paths persist completion to DB

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/server/index.ts

@@ -5,6 +5,7 @@ import { itemRoutes } from "./routes/items.ts";
 import { categoryRoutes } from "./routes/categories.ts";
 import { totalRoutes } from "./routes/totals.ts";
 import { imageRoutes } from "./routes/images.ts";
+import { settingsRoutes } from "./routes/settings.ts";
 
 // Seed default data on startup
 seedDefaults();
@@ -21,6 +22,7 @@ app.route("/api/items", itemRoutes);
 app.route("/api/categories", categoryRoutes);
 app.route("/api/totals", totalRoutes);
 app.route("/api/images", imageRoutes);
+app.route("/api/settings", settingsRoutes);
 
 // Serve uploaded images
 app.use("/uploads/*", serveStatic({ root: "./" }));