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/schemas.ts

@@ -0,0 +1,25 @@
+import { z } from "zod";
+
+export const createItemSchema = z.object({
+  name: z.string().min(1, "Name is required"),
+  weightGrams: z.number().nonnegative().optional(),
+  priceCents: z.number().int().nonnegative().optional(),
+  categoryId: z.number().int().positive(),
+  notes: z.string().optional(),
+  productUrl: z.string().url().optional().or(z.literal("")),
+});
+
+export const updateItemSchema = createItemSchema.partial().extend({
+  id: z.number().int().positive(),
+});
+
+export const createCategorySchema = z.object({
+  name: z.string().min(1, "Category name is required"),
+  emoji: z.string().min(1).max(4).default("\u{1F4E6}"),
+});
+
+export const updateCategorySchema = z.object({
+  id: z.number().int().positive(),
+  name: z.string().min(1).optional(),
+  emoji: z.string().min(1).max(4).optional(),
+});