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>

tests/helpers/db.ts

@@ -0,0 +1,49 @@
+import { Database } from "bun:sqlite";
+import { drizzle } from "drizzle-orm/bun-sqlite";
+import * as schema from "../../src/db/schema.ts";
+
+export function createTestDb() {
+  const sqlite = new Database(":memory:");
+  sqlite.run("PRAGMA foreign_keys = ON");
+
+  // Create tables matching the Drizzle schema
+  sqlite.run(`
+    CREATE TABLE categories (
+      id INTEGER PRIMARY KEY AUTOINCREMENT,
+      name TEXT NOT NULL UNIQUE,
+      emoji TEXT NOT NULL DEFAULT '📦',
+      created_at INTEGER NOT NULL DEFAULT (unixepoch())
+    )
+  `);
+
+  sqlite.run(`
+    CREATE TABLE items (
+      id INTEGER PRIMARY KEY AUTOINCREMENT,
+      name TEXT NOT NULL,
+      weight_grams REAL,
+      price_cents INTEGER,
+      category_id INTEGER NOT NULL REFERENCES categories(id),
+      notes TEXT,
+      product_url TEXT,
+      image_filename TEXT,
+      created_at INTEGER NOT NULL DEFAULT (unixepoch()),
+      updated_at INTEGER NOT NULL DEFAULT (unixepoch())
+    )
+  `);
+
+  sqlite.run(`
+    CREATE TABLE settings (
+      key TEXT PRIMARY KEY,
+      value TEXT NOT NULL
+    )
+  `);
+
+  const db = drizzle(sqlite, { schema });
+
+  // Seed default Uncategorized category
+  db.insert(schema.categories)
+    .values({ name: "Uncategorized", emoji: "\u{1F4E6}" })
+    .run();
+
+  return db;
+}