feat: add pino logger with file and stdout transports

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/logger.ts

@@ -0,0 +1,28 @@
+import pino from "pino";
+import { mkdirSync } from "node:fs";
+import { join } from "node:path";
+
+export function createLogger(logDir?: string): pino.Logger {
+  if (!logDir) {
+    return pino({ level: "info" });
+  }
+
+  mkdirSync(logDir, { recursive: true });
+
+  const transport = pino.transport({
+    targets: [
+      {
+        target: "pino/file",
+        options: { destination: 1 }, // stdout
+        level: "info",
+      },
+      {
+        target: "pino/file",
+        options: { destination: join(logDir, "bot.log"), mkdir: true },
+        level: "debug",
+      },
+    ],
+  });
+
+  return pino({ level: "debug" }, transport);
+}