polish the api route, response, health, cache, and metrics

app/helpers/logger.php

@@ -0,0 +1,28 @@
+<?php
+// Simple file logger
+function log_start() {
+  $id = bin2hex(random_bytes(4));
+  $GLOBALS['req_start'] = microtime(true);
+  header("X-Request-Id: $id");
+  return $id;
+}
+function log_end($id, $status=200) {
+  $ms = round((microtime(true)-$GLOBALS['req_start'])*1000);
+  $ip = $_SERVER['REMOTE_ADDR'] ?? '-';
+  $path = $_SERVER['REQUEST_URI'] ?? '-';
+  $plan = $_SERVER['HTTP_X_DEWEMOJI_PLAN'] ?? ($GLOBALS['bucket_plan'] ?? '-');
+  $bucket = $GLOBALS['bucket_id'] ?? '-';
+  $ua = $_SERVER['HTTP_USER_AGENT'] ?? '-';
+  $ref = $_SERVER['HTTP_REFERER'] ?? '-';
+  $errorMsg = '';
+  if ($status >= 400) {
+    $errorMsg = $GLOBALS['json_error_msg'] ?? '';
+  }
+  $line = sprintf("[%s] %s %s %s plan=%s bucket=%s %d %dms ua=\"%s\" ref=\"%s\"%s\n",
+    gmdate('c'), $id, $ip, $path, $plan, $bucket, $status, $ms, $ua, $ref,
+    $errorMsg ? " error=\"".addslashes($errorMsg)."\"" : ''
+  );
+  $logFile = __DIR__.'/../../storage/logs/access.log';
+  @mkdir(dirname($logFile), 0775, true);
+  error_log($line, 3, $logFile);
+}