feat: add touch driver abstraction layer

XPT2046 path: no change — uses TFT_eSPI built-in getTouch().
GT911 path:   TouchDriver namespace with begin()/read() stub.

TouchDriverGT911.cpp compiles to nothing on TFT_eSPI targets.
Uncomment TAMC_GT911 lines to enable real capacitive touch.

sketches/doorbell-touch-esp32-32e/TouchDriver.h

@@ -0,0 +1,21 @@
+#pragma once
+#include "BoardConfig.h"
+
+// ═══════════════════════════════════════════════════════════════════
+// Touch driver abstraction
+//
+// XPT2046: integrated in TFT_eSPI — DisplayManager calls
+//          _tft.getTouch() / _tft.setTouch() directly inside
+//          #if USE_TOUCH_XPT2046 blocks.
+//
+// GT911:   separate I2C controller — namespace below.
+// ═══════════════════════════════════════════════════════════════════
+
+#if USE_TOUCH_GT911
+
+namespace TouchDriver {
+  void begin();
+  bool read(uint16_t &x, uint16_t &y);
+}
+
+#endif