refactor(backend): split log files into separate file

lib/log/constants.ts

@@ -0,0 +1,14 @@
+import * as env from "@lib/env.ts";
+import { ensureDir } from "https://deno.land/std@0.224.0/fs/mod.ts";
+import { join } from "node:path";
+import { getLogLevel, LOG_LEVEL } from "@lib/log/types.ts";
+
+export const LOG_DIR = join(env.DATA_DIR, "logs");
+
+// Ensure the log directory exists
+await ensureDir(LOG_DIR);
+
+export let logLevel = getLogLevel(env.LOG_LEVEL);
+export function setLogLevel(level: LOG_LEVEL) {
+  logLevel = level;
+}