Integrate Monolog: replace four logging systems with single PSR-3 factory

- Add monolog/monolog dependency (^3.10)  
- Create app/Logger.php central factory with channels: app, admin, error, audit
- Each channel gets RotatingFileHandler (30-day retention) with pass-through LineFormatter
  preserving existing JSON format contracts
- Rewrite AppLogger as thin facade delegating to Logger::get('app')
- Rewrite ErrorHandler::log() to delegate to Logger::get('error')
- Rewrite AdminLogger file output to delegate to Logger::get('admin'), keep DB writes
- Add Monolog file shadow to Audit via Logger::get('audit') (Option A per monolog-plan)
- Log level controlled by LOG_LEVEL env var (defaults: DEBUG in cli-server, WARNING otherwise)
- Graceful NullHandler fallback when log directory is not writable
- Update SystemController LOG_FILES: remove php_error, add app/admin/error/audit
- JSON app logs parsed to readable one-liners in the log viewer
- Remove nginx config tab (parametres + fragment + template + css)
- Friendly empty-state message when app log files don't exist yet (notYet)
- PHP tail fallback when exec() unavailable
- All 228 PHPUnit tests pass, no call sites changed

app/src/Audit.php

@@ -34,6 +34,7 @@ class Audit
         ?array $oldData = null,
         ?array $newData = null
     ): void {
+        // DB write is the primary path — best-effort, never crash.
         try {
             $stmt = $db->getConnection()->prepare(
                 'INSERT INTO audit_log (actor, action, table_name, record_id, old_data, new_data)
@@ -49,7 +50,33 @@ class Audit
             ]);
         } catch (\Throwable $e) {
             // Audit logging is best-effort — never crash the app over it.
-            error_log('[Audit] write failed: ' . $e->getMessage());
+            error_log('[Audit] DB write failed: ' . $e->getMessage());
+        }
+
+        // File shadow — structured JSON-line log for debuggability
+        // (Option A from monolog-plan: keep Audit DB logic as-is, add file trace)
+        try {
+            $entry = [
+                'timestamp' => date('c'),
+                'ip'        => $_SERVER['REMOTE_ADDR'] ?? 'cli',
+                'user_agent' => $_SERVER['HTTP_USER_AGENT'] ?? '',
+                'actor'     => $actor,
+                'action'    => $action,
+                'table'     => $tableName,
+                'record_id' => $recordId,
+            ];
+            if ($oldData !== null) {
+                $entry['old_data'] = $oldData;
+            }
+            if ($newData !== null) {
+                $entry['new_data'] = $newData;
+            }
+
+            $line = json_encode($entry, JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE);
+            Logger::get('audit')->info($line);
+        } catch (\Throwable $e) {
+            // File shadow is also best-effort
+            error_log('[Audit] file shadow write failed: ' . $e->getMessage());
         }
     }