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/shared/types.ts

@@ -0,0 +1,18 @@
+import type { z } from "zod";
+import type {
+  createItemSchema,
+  updateItemSchema,
+  createCategorySchema,
+  updateCategorySchema,
+} from "./schemas.ts";
+import type { items, categories } from "../db/schema.ts";
+
+// Types inferred from Zod schemas
+export type CreateItem = z.infer<typeof createItemSchema>;
+export type UpdateItem = z.infer<typeof updateItemSchema>;
+export type CreateCategory = z.infer<typeof createCategorySchema>;
+export type UpdateCategory = z.infer<typeof updateCategorySchema>;
+
+// Types inferred from Drizzle schema
+export type Item = typeof items.$inferSelect;
+export type Category = typeof categories.$inferSelect;