feat(01-01): add database schema, shared Zod schemas, seed, and test infrastructure

- Create Drizzle schema with items, categories, and settings tables
- Set up database connection singleton with WAL mode and foreign keys
- Add seed script for default Uncategorized category
- Create shared Zod validation schemas for items and categories
- Export TypeScript types inferred from Zod and Drizzle schemas
- Add in-memory SQLite test helper for isolated test databases
- Wire seed into Hono server startup

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

src/server/index.ts

@@ -1,5 +1,9 @@
 import { Hono } from "hono";
 import { serveStatic } from "hono/bun";
+import { seedDefaults } from "../db/seed.ts";
+
+// Seed default data on startup
+seedDefaults();
 
 const app = new Hono();