feat: sistema di log rotante 4 livelli (EverLog + LoggingPDO)

- api/logger.php: EverLog static class con 4 livelli (DEBUG/INFO/WARN/ERROR)
  - Rotazione oraria/giornaliera configurabile via LOG_ROTATE_HOURS
  - Max file configurabile via LOG_MAX_FILES (default 14)
  - Request ID unico per tracciare ogni chiamata API
  - EverLog::query(), aiCall(), aiResponse(), cache(), slowOp(), exception()
  - Endpoint get_logs per inspection remota (protetto da SETTINGS_TOKEN)
  - LoggingPDO + LoggingPDOStatement: auto-log di OGNI query SQLite
- api/database.php: getDB() restituisce LoggingPDO (drop-in, retrocompat.)
- api/index.php: EverLog integrato in ~82 punti
  - Entry log in ogni funzione API
  - callGemini/callGeminiWithFallback: timing AI + aiCall/aiResponse
  - Rate limiter, unknown action, errori globali, DB connect fail

Livello default: INFO (query DB a DEBUG, solo se LOG_LEVEL=DEBUG)

api/database.php

@@ -40,8 +40,13 @@ function _ensureDataDir(): void {
 
 function getDB(): PDO {
     _ensureDataDir();
+    // logger.php is required by index.php before getDB() is called.
+    // In cron context it may not be loaded yet — guard with class_exists.
+    $useLogging = class_exists('LoggingPDO', false);
     $isNew = !file_exists(DB_PATH);
-    $db = new PDO('sqlite:' . DB_PATH);
+    $db = $useLogging
+        ? new LoggingPDO('sqlite:' . DB_PATH)
+        : new PDO('sqlite:' . DB_PATH);
     $db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
     $db->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC);
     $db->exec("PRAGMA journal_mode=WAL");