feat: button handler with press detection and combo support

Co-authored-by: Cursor <cursoragent@cursor.com>

src/button_handler.h

@@ -0,0 +1,38 @@
+#pragma once
+
+#include <Arduino.h>
+#include "config.h"
+
+class PowerManager;
+class SettingsManager;
+
+enum class ButtonEvent : uint8_t {
+    None,
+    NextPhoto,
+    RandomPhoto,
+    PlayPause,
+    DeepSleep,
+    FactoryReset
+};
+
+class ButtonHandler {
+public:
+    void begin(PowerManager& power, SettingsManager& settings);
+    ButtonEvent poll();
+
+private:
+    PowerManager* _power = nullptr;
+    SettingsManager* _settings = nullptr;
+
+    unsigned long _btnTopPressTime = 0;
+    unsigned long _btnUpPressTime = 0;
+    unsigned long _btnDownPressTime = 0;
+
+    bool _btnTopPressed = false;
+    bool _btnUpPressed = false;
+    bool _btnDownPressed = false;
+
+    unsigned long _lastDebounce = 0;
+
+    bool debounced(unsigned long now);
+};