overheat monitor with auto poweroff

- needs passwordless sudo on target machine or deploy to run as root

pi/ui/lib/services/config_service.dart

@@ -0,0 +1,69 @@
+import 'dart:convert';
+import 'dart:io';
+
+/// Configuration service - loads and caches values from config.json
+///
+/// Uses singleton pattern. Falls back to defaults if config file missing.
+class ConfigService {
+  ConfigService._();
+  static final instance = ConfigService._();
+
+  // Loaded config cache
+  Map<String, dynamic>? _config;
+  bool _loaded = false;
+
+  // Defaults
+  static const double _defaultThreshold = 80.0;
+  static const int _defaultTriggerDuration = 10;
+  static const int _defaultShutdownDelay = 10;
+
+  /// Load config from JSON file
+  ///
+  /// Looks for config.json in same directory as executable.
+  /// Safe to call multiple times - only loads once.
+  Future<void> load() async {
+    if (_loaded) return;
+
+    try {
+      // Config file sits next to the executable
+      final exePath = Platform.resolvedExecutable;
+      final exeDir = File(exePath).parent.path;
+      final configPath = '$exeDir${Platform.pathSeparator}config.json';
+
+      final file = File(configPath);
+      if (await file.exists()) {
+        final content = await file.readAsString();
+        _config = jsonDecode(content) as Map<String, dynamic>;
+      }
+    } catch (e) {
+      // Config parse error - fall back to defaults
+      _config = null;
+    }
+
+    _loaded = true;
+  }
+
+  /// CPU temperature threshold in Celsius
+  double get overheatThreshold {
+    final overheat = _config?['overheat'] as Map<String, dynamic>?;
+    final value = overheat?['threshold_celsius'];
+    if (value is num) return value.toDouble();
+    return _defaultThreshold;
+  }
+
+  /// How long temp must exceed threshold before triggering
+  Duration get overheatTriggerDuration {
+    final overheat = _config?['overheat'] as Map<String, dynamic>?;
+    final value = overheat?['trigger_duration_sec'];
+    if (value is int) return Duration(seconds: value);
+    return Duration(seconds: _defaultTriggerDuration);
+  }
+
+  /// Countdown before shutdown after overheat triggers
+  Duration get shutdownDelay {
+    final overheat = _config?['overheat'] as Map<String, dynamic>?;
+    final value = overheat?['shutdown_delay_sec'];
+    if (value is int) return Duration(seconds: value);
+    return Duration(seconds: _defaultShutdownDelay);
+  }
+}