fix(logging): fix static setLogService and null handling

apps/lib/core/logging/log_entry.dart

@@ -51,7 +51,7 @@ class LogEntry {
     final sb = StringBuffer();
     sb.writeln('[$timestamp] ${level.name.toUpperCase()} [$module]');
     if (funcName != null || lineNo != null) {
-      sb.write('  at $funcName' ?? '');
+      sb.write('  at ${funcName ?? ''}');
       if (lineNo != null) sb.write(':$lineNo');
       sb.writeln();
     }

apps/lib/core/logging/logger.dart

@@ -2,14 +2,6 @@ import 'log_service.dart';
 
 LogService? _globalLogService;
 
-void setLogService(LogService service) {
-  _globalLogService = service;
-}
-
-LogService _ensureService() {
-  return _globalLogService ?? (throw StateError('LogService not initialized'));
-}
-
 class Logger {
   final String module;
   final LogService _service;
@@ -20,6 +12,15 @@ class Logger {
     return Logger(module, _ensureService());
   }
 
+  static void setLogService(LogService service) {
+    _globalLogService = service;
+  }
+
+  static LogService _ensureService() {
+    return _globalLogService ??
+        (throw StateError('LogService not initialized'));
+  }
+
   void debug({
     required String message,
     Map<String, dynamic>? extra,