v1.2.0: Firmware refactor to service-oriented architecture + WiFi fixes

Firmware:
- Fixed WiFi reconnection bug after power cycle by adding WiFi.persistent(false)
  and disabling auto-connect/auto-reconnect
- Fixed AP mode not broadcasting by properly handling WIFI_AP_STA mode transitions
- Refactored to service-oriented architecture:
  - device_state: Central state management with event callbacks
  - config_service: NVS persistence (renamed from config_manager)
  - wifi_service: WiFi STA/AP management (extracted from main.cpp)
  - mqtt_service: MQTT client and message routing (extracted from main.cpp)
  - ble_service: BLE GATT services (renamed from ble_services)
  - web_service: HTTP configuration portal (renamed from web_portal)
- main.cpp reduced from ~470 lines to ~60 lines (thin orchestrator)
- Each service is self-contained with setup()/loop() pattern

Backend:
- Added heart rate variation endpoint
- UI improvements

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

firmware/esp32_ble_sim/include/device_state.h

@@ -0,0 +1,105 @@
+#ifndef DEVICE_STATE_H
+#define DEVICE_STATE_H
+
+#include <Arduino.h>
+#include <functional>
+
+// ============================================
+// Device Types
+// ============================================
+enum class DeviceType {
+    NONE,
+    HEART_RATE,
+    TREADMILL
+};
+
+// ============================================
+// Connection State
+// ============================================
+struct ConnectionState {
+    bool wifiConnected = false;
+    bool mqttConnected = false;
+    bool bleClientConnected = false;
+    String ipAddress = "";
+};
+
+// ============================================
+// Simulated Device Values
+// ============================================
+struct SimulatedValues {
+    // Heart Rate Monitor
+    uint8_t heartRate = 70;
+    uint8_t batteryLevel = 100;
+
+    // Treadmill
+    uint16_t treadmillSpeed = 0;      // 0.01 km/h resolution
+    int16_t treadmillIncline = 0;     // 0.1% resolution
+    uint32_t treadmillDistance = 0;   // meters
+    float distanceAccumulator = 0.0;  // fractional distance
+};
+
+// ============================================
+// Event Callbacks
+// ============================================
+using DeviceTypeChangedCallback = std::function<void(DeviceType newType)>;
+using ValuesChangedCallback = std::function<void(const SimulatedValues& values)>;
+using ConnectionChangedCallback = std::function<void(const ConnectionState& state)>;
+
+// ============================================
+// Device State Manager (Singleton)
+// ============================================
+class DeviceState {
+public:
+    static DeviceState& getInstance();
+
+    // Prevent copying
+    DeviceState(const DeviceState&) = delete;
+    DeviceState& operator=(const DeviceState&) = delete;
+
+    // Device type
+    DeviceType getDeviceType() const { return deviceType; }
+    void setDeviceType(DeviceType type);
+    bool isBleStarted() const { return deviceType != DeviceType::NONE; }
+    const char* getDeviceTypeString() const;
+
+    // Simulated values
+    const SimulatedValues& getValues() const { return values; }
+    void setHeartRate(uint8_t bpm);
+    void setBatteryLevel(uint8_t level);
+    void setTreadmillSpeed(float speedKmh);
+    void setTreadmillIncline(float inclinePercent);
+    void setTreadmillDistance(uint32_t meters);
+    void resetTreadmillDistance();
+    void accumulateTreadmillDistance(float deltaSeconds);
+
+    // Connection state
+    const ConnectionState& getConnectionState() const { return connectionState; }
+    void setWifiConnected(bool connected, const String& ip = "");
+    void setMqttConnected(bool connected);
+    void setBleClientConnected(bool connected);
+
+    // Event registration
+    void onDeviceTypeChanged(DeviceTypeChangedCallback callback);
+    void onValuesChanged(ValuesChangedCallback callback);
+    void onConnectionChanged(ConnectionChangedCallback callback);
+
+private:
+    DeviceState() = default;
+
+    DeviceType deviceType = DeviceType::NONE;
+    SimulatedValues values;
+    ConnectionState connectionState;
+
+    // Callbacks
+    DeviceTypeChangedCallback deviceTypeCallback = nullptr;
+    ValuesChangedCallback valuesCallback = nullptr;
+    ConnectionChangedCallback connectionCallback = nullptr;
+
+    void notifyValuesChanged();
+    void notifyConnectionChanged();
+};
+
+// Convenience macro for accessing singleton
+#define deviceState DeviceState::getInstance()
+
+#endif // DEVICE_STATE_H