touch: idle power-save — loop-throttle + downclock when parked (#19)

Opt-in Idle power-save for the T-Deck: when parked (screen off, on battery, no
companion client, Wi-Fi+BLE off, mesh idle) the main loop is throttled with
vTaskDelay so the FreeRTOS idle task can halt the CPU between ticks, on top of the
existing 80 MHz screen-off downclock — without ever stopping mesh RX. Default OFF
(Settings -> Lock, persisted TouchCfg v8 sleep_idle); status-bar moon indicator +
idle stats. Heltec V4 compiles (gate never passes there). A plain scheduler throttle
rather than esp_light_sleep_start(), which trips INT_WDT in this build.

Co-authored-by: Dan Vybiral <dan.vybiral@greencode.cz>

src/main.cpp

@@ -12,6 +12,7 @@
 #include "helpers/esp32/SdNvsPrefs.h"        // route prefs to file storage (SD/SPIFFS), off NVS
                                              // (quoted: use wadamesh's src/ copy, not the lib's stale one)
 #include "wadamesh_mark_rgb.h"               // anti-aliased mesh-mark (RGB565) for the pre-LVGL boot screen
+#include "ui-touch/TouchSleep.h"             // idle light-sleep controller (loopEnd called at end of loop())
 #endif
 
 // Believe it or not, this std C function is busted on some platforms!
@@ -672,4 +673,11 @@ void loop() {
 #if defined(ESP32_PLATFORM)
   board.pollHttpOtaReboot();
 #endif
+
+#if defined(HAS_TOUCH_UI)
+  // Idle light-sleep gate: evaluated every loop tick. g_enabled is false by
+  // default (Task 1 is inert); Task 2 sets it from the NVS pref and wires
+  // the real predicates so the gate can actually pass and arm light sleep.
+  touchSleep::loopEnd(millis());
+#endif
 }