feat(db): drizzle-schema, db-client und initiale migration

Vollstaendiges Datenmodell: Katalog (manufacturer, theme, set, tag,
instruction), Besitz (collection_item, location, missing_part, photo),
Wunschlisten (wishlist, wishlist_item) und die Auth-Tabellen von
better-auth inklusive passkey und invite.

Kernregel: ein set ist ein Katalogeintrag, ein collection_item die
Verknuepfung mit dem tatsaechlichen Besitz. Preise liegen als Cent in
INTEGER-Spalten, damit Summen exakt bleiben.

SQLite laeuft mit WAL, foreign_keys=ON und busy_timeout.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/db/index.ts

@@ -0,0 +1,41 @@
+import fs from 'node:fs';
+import Database from 'better-sqlite3';
+import { drizzle } from 'drizzle-orm/better-sqlite3';
+import { env } from '@/env';
+import * as schema from './schema';
+
+/**
+ * SQLite connection for the whole app.
+ *
+ * Cached on globalThis so Next's dev-mode module reloading does not open a new
+ * file handle on every hot reload.
+ */
+function createConnection() {
+  fs.mkdirSync(env.DB_DIR, { recursive: true });
+
+  const sqlite = new Database(env.DB_PATH);
+  // WAL keeps readers from blocking the single writer - required for a server
+  // that renders pages while a background action writes.
+  sqlite.pragma('journal_mode = WAL');
+  // NORMAL is the recommended durability level in WAL mode.
+  sqlite.pragma('synchronous = NORMAL');
+  // SQLite has foreign keys off by default; our schema relies on them.
+  sqlite.pragma('foreign_keys = ON');
+  // Wait instead of throwing SQLITE_BUSY when another write is in flight.
+  sqlite.pragma('busy_timeout = 5000');
+
+  return drizzle(sqlite, { schema });
+}
+
+const globalForDb = globalThis as unknown as {
+  bricktrackDb?: ReturnType<typeof createConnection>;
+};
+
+export const db = globalForDb.bricktrackDb ?? createConnection();
+
+if (!env.isProduction) {
+  globalForDb.bricktrackDb = db;
+}
+
+export { schema };
+export type Db = typeof db;