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/db/schema.ts

@@ -0,0 +1,34 @@
+import { sqliteTable, text, integer, real } from "drizzle-orm/sqlite-core";
+
+export const categories = sqliteTable("categories", {
+  id: integer("id").primaryKey({ autoIncrement: true }),
+  name: text("name").notNull().unique(),
+  emoji: text("emoji").notNull().default("\u{1F4E6}"),
+  createdAt: integer("created_at", { mode: "timestamp" })
+    .notNull()
+    .$defaultFn(() => new Date()),
+});
+
+export const items = sqliteTable("items", {
+  id: integer("id").primaryKey({ autoIncrement: true }),
+  name: text("name").notNull(),
+  weightGrams: real("weight_grams"),
+  priceCents: integer("price_cents"),
+  categoryId: integer("category_id")
+    .notNull()
+    .references(() => categories.id),
+  notes: text("notes"),
+  productUrl: text("product_url"),
+  imageFilename: text("image_filename"),
+  createdAt: integer("created_at", { mode: "timestamp" })
+    .notNull()
+    .$defaultFn(() => new Date()),
+  updatedAt: integer("updated_at", { mode: "timestamp" })
+    .notNull()
+    .$defaultFn(() => new Date()),
+});
+
+export const settings = sqliteTable("settings", {
+  key: text("key").primaryKey(),
+  value: text("value").notNull(),
+});