feat: project scaffolding and env config loader

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/config.js

@@ -0,0 +1,27 @@
+import 'dotenv/config';
+
+const REQUIRED_VARS = ['STORAGE_DIR', 'DB_HOST', 'DB_USER', 'DB_PASSWORD', 'DB_NAME'];
+
+export function loadConfig() {
+  const missing = REQUIRED_VARS.filter((key) => !process.env[key]);
+  if (missing.length > 0) {
+    throw new Error(`Missing required environment variables: ${missing.join(', ')}`);
+  }
+
+  return {
+    port: Number(process.env.PORT ?? 3000),
+    storageDir: process.env.STORAGE_DIR,
+    db: {
+      host: process.env.DB_HOST,
+      user: process.env.DB_USER,
+      password: process.env.DB_PASSWORD,
+      database: process.env.DB_NAME,
+    },
+    maxFileSizeMb: Number(process.env.MAX_FILE_SIZE_MB ?? 100),
+    retentionHours: Number(process.env.RETENTION_HOURS ?? 1),
+    workerPollIntervalMs: Number(process.env.WORKER_POLL_INTERVAL_MS ?? 1500),
+    workerConcurrency: Number(process.env.WORKER_CONCURRENCY ?? 3),
+    rateLimitMaxJobs: Number(process.env.RATE_LIMIT_MAX_JOBS ?? 20),
+    rateLimitWindowMinutes: Number(process.env.RATE_LIMIT_WINDOW_MINUTES ?? 10),
+  };
+}