Add touch-down and long-press input detection

Implement touch-down event detection to provide immediate visual feedback when touching list items, mirroring button navigation behavior. Add long-press detection (500ms threshold) to distinguish between tap and hold gestures. Apply touch-down selection updates to file browser, home menu, and recent books activities.

src/network/TaskWatchdog.h

@@ -0,0 +1,21 @@
+#pragma once
+
+#include <esp_task_wdt.h>
+
+// Feed the Task Watchdog Timer only when the calling task is actually
+// subscribed to it. esp_task_wdt_reset() logs
+//   "task_wdt: esp_task_wdt_reset(...): task not found"
+// on every call when the current task was never registered via
+// esp_task_wdt_add(). Whether the Arduino loopTask is auto-subscribed depends
+// on the chip target's framework sdkconfig: the ESP32-C3 (X4) build subscribes
+// it, the classic-ESP32 (m5paper) build does not, so the unguarded resets in
+// the web server / WiFi paths spammed the log there.
+//
+// esp_task_wdt_status(nullptr) returns ESP_OK only when the current task is
+// subscribed, so this guard makes the reset a no-op on builds where the loop
+// task is not watchdog-monitored, while preserving the reset where it is.
+static inline void feedTaskWatchdog() {
+  if (esp_task_wdt_status(nullptr) == ESP_OK) {
+    esp_task_wdt_reset();
+  }
+}