Long-press trackball blanks screen; suppress touch wakes when off

Two pocket-carry quality-of-life additions:

1. Long-press (1.2s) trackball click blanks the screen if no LVGL
   screen consumes the long-press. InputManager captures the power
   state at click DOWN (_clickFromScreenOn) and only emits the
   long-press if the screen was already on, so a long-press from
   SCREEN_OFF wakes without immediately re-blanking.

2. Touch events are ignored entirely while screen is off, preventing
   accidental wakes from pressure on the panel in a pocket/bag.
   Trackball click and keyboard keys still wake normally.

InputManager now holds a Power* injected via setPowerMgr() in setup.

src/main.cpp

@@ -435,6 +435,7 @@ void setup() {
 
     // Step 10: Input manager
     inputManager.begin(&keyboard, &trackball, &touch);
+    inputManager.setPowerMgr(&powerMgr);
 
     // Step 10.5: LVGL input drivers
     LvInput::init(&keyboard, &trackball, &touch);
@@ -933,9 +934,11 @@ void loop() {
         powerMgr.weakActivity();   // Trackball: wake from dim only
     }
 
-    // 2. Long-press dispatch
+    // 2. Long-press dispatch — screen blanking is the default if no screen consumes it
     if (inputManager.hadLongPress()) {
-        ui.handleLongPress();
+        if (!ui.handleLongPress()) {
+            powerMgr.forceScreenOff();
+        }
     }
 
     // 3. Key event dispatch