refactor: Simplify XtcReaderActivity with detectPageTurn (#1837)

## Summary

Simplify duplicated code in `XtcReaderActivity` to use
`ReaderUtils::detectPageTurn`. This implementation is now shared with
`EpubReaderActivity` and `TxtReaderActivity`. Also deduplicated the
chapter skip time constant.

---

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src/activities/reader/EpubReaderActivity.cpp

@@ -30,7 +30,6 @@
 
 namespace {
 // pagesPerRefresh now comes from SETTINGS.getRefreshFrequency()
-constexpr unsigned long skipChapterMs = 700;
 // pages per minute, first item is 1 to prevent division by zero if accessed
 constexpr int PAGE_TURN_RATES[] = {1, 1, 3, 6, 12};
 
@@ -185,7 +184,7 @@ void EpubReaderActivity::loop() {
     return;
   }
 
-  auto [prevTriggered, nextTriggered, fromTilt] = ReaderUtils::detectPageTurn(mappedInput);
+  const auto [prevTriggered, nextTriggered, fromTilt] = ReaderUtils::detectPageTurn(mappedInput);
   if (!prevTriggered && !nextTriggered) {
     return;
   }
@@ -203,7 +202,7 @@ void EpubReaderActivity::loop() {
     return;
   }
 
-  const bool longPress = !fromTilt && mappedInput.getHeldTime() > skipChapterMs;
+  const bool longPress = !fromTilt && mappedInput.getHeldTime() > ReaderUtils::SKIP_HOLD_MS;
 
   // Don't skip chapter after screenshot
   if (gpio.wasReleased(HalGPIO::BTN_POWER) && gpio.wasReleased(HalGPIO::BTN_DOWN)) {

src/activities/reader/ReaderUtils.h

@@ -10,6 +10,7 @@
 namespace ReaderUtils {
 
 constexpr unsigned long GO_HOME_MS = 1000;
+constexpr unsigned long SKIP_HOLD_MS = 700;
 
 inline void applyOrientation(GfxRenderer& renderer, const uint8_t orientation) {
   switch (orientation) {

src/activities/reader/TxtReaderActivity.cpp

@@ -71,7 +71,7 @@ void TxtReaderActivity::loop() {
     return;
   }
 
-  auto [prevTriggered, nextTriggered, fromTilt] = ReaderUtils::detectPageTurn(mappedInput);
+  const auto [prevTriggered, nextTriggered, fromTilt] = ReaderUtils::detectPageTurn(mappedInput);
   if (!prevTriggered && !nextTriggered) {
     return;
   }

src/activities/reader/XtcReaderActivity.cpp

@@ -10,22 +10,17 @@
 #include <FsHelpers.h>
 #include <GfxRenderer.h>
 #include <HalStorage.h>
-#include <HalTiltSensor.h>
 #include <I18n.h>
 
 #include "CrossPointSettings.h"
 #include "CrossPointState.h"
 #include "MappedInputManager.h"
+#include "ReaderUtils.h"
 #include "RecentBooksStore.h"
 #include "XtcReaderChapterSelectionActivity.h"
 #include "components/UITheme.h"
 #include "fontIds.h"
 
-namespace {
-constexpr unsigned long skipPageMs = 700;
-constexpr unsigned long goHomeMs = 1000;
-}  // namespace
-
 void XtcReaderActivity::onEnter() {
   Activity::onEnter();
 
@@ -70,34 +65,19 @@ void XtcReaderActivity::loop() {
   }
 
   // Long press BACK (1s+) goes to file selection
-  if (mappedInput.isPressed(MappedInputManager::Button::Back) && mappedInput.getHeldTime() >= goHomeMs) {
+  if (mappedInput.isPressed(MappedInputManager::Button::Back) && mappedInput.getHeldTime() >= ReaderUtils::GO_HOME_MS) {
     activityManager.goToFileBrowser(xtc ? xtc->getPath() : "");
     return;
   }
 
   // Short press BACK goes directly to home
-  if (mappedInput.wasReleased(MappedInputManager::Button::Back) && mappedInput.getHeldTime() < goHomeMs) {
+  if (mappedInput.wasReleased(MappedInputManager::Button::Back) &&
+      mappedInput.getHeldTime() < ReaderUtils::GO_HOME_MS) {
     onGoHome();
     return;
   }
 
-  // When long-press chapter skip is disabled, turn pages on press instead of release.
-  const bool usePressForPageTurn = SETTINGS.longPressButtonBehavior == SETTINGS.OFF;
-  const bool tiltNext = SETTINGS.tiltPageTurn && halTiltSensor.wasTiltedForward();
-  const bool tiltPrev = SETTINGS.tiltPageTurn && halTiltSensor.wasTiltedBack();
-  const bool prevTriggered =
-      tiltPrev || (usePressForPageTurn ? (mappedInput.wasPressed(MappedInputManager::Button::PageBack) ||
-                                          mappedInput.wasPressed(MappedInputManager::Button::Left))
-                                       : (mappedInput.wasReleased(MappedInputManager::Button::PageBack) ||
-                                          mappedInput.wasReleased(MappedInputManager::Button::Left)));
-  const bool powerPageTurn = SETTINGS.shortPwrBtn == CrossPointSettings::SHORT_PWRBTN::PAGE_TURN &&
-                             mappedInput.wasReleased(MappedInputManager::Button::Power);
-  const bool nextTriggered =
-      tiltNext || (usePressForPageTurn ? (mappedInput.wasPressed(MappedInputManager::Button::PageForward) ||
-                                          powerPageTurn || mappedInput.wasPressed(MappedInputManager::Button::Right))
-                                       : (mappedInput.wasReleased(MappedInputManager::Button::PageForward) ||
-                                          powerPageTurn || mappedInput.wasReleased(MappedInputManager::Button::Right)));
-
+  const auto [prevTriggered, nextTriggered, fromTilt] = ReaderUtils::detectPageTurn(mappedInput);
   if (!prevTriggered && !nextTriggered) {
     return;
   }
@@ -113,9 +93,8 @@ void XtcReaderActivity::loop() {
     return;
   }
 
-  const bool fromTilt = tiltPrev || tiltNext;
-  const bool skipPages =
-      !fromTilt && SETTINGS.longPressButtonBehavior == SETTINGS.CHAPTER_SKIP && mappedInput.getHeldTime() > skipPageMs;
+  const bool skipPages = !fromTilt && SETTINGS.longPressButtonBehavior == SETTINGS.CHAPTER_SKIP &&
+                         mappedInput.getHeldTime() > ReaderUtils::SKIP_HOLD_MS;
   const int skipAmount = skipPages ? 10 : 1;
 
   if (prevTriggered) {
@@ -242,14 +221,7 @@ void XtcReaderActivity::renderPage() {
       }
     }
 
-    // Display BW with conditional refresh based on pagesUntilFullRefresh
-    if (pagesUntilFullRefresh <= 1) {
-      renderer.displayBuffer(HalDisplay::HALF_REFRESH);
-      pagesUntilFullRefresh = SETTINGS.getRefreshFrequency();
-    } else {
-      renderer.displayBuffer();
-      pagesUntilFullRefresh--;
-    }
+    ReaderUtils::displayWithRefreshCycle(renderer, pagesUntilFullRefresh);
 
     // Pass 2: LSB buffer - mark DARK gray only (XTH value 1)
     // In LUT: 0 bit = apply gray effect, 1 bit = untouched
@@ -321,14 +293,7 @@ void XtcReaderActivity::renderPage() {
 
   // XTC pages already have status bar pre-rendered, no need to add our own
 
-  // Display with appropriate refresh
-  if (pagesUntilFullRefresh <= 1) {
-    renderer.displayBuffer(HalDisplay::HALF_REFRESH);
-    pagesUntilFullRefresh = SETTINGS.getRefreshFrequency();
-  } else {
-    renderer.displayBuffer();
-    pagesUntilFullRefresh--;
-  }
+  ReaderUtils::displayWithRefreshCycle(renderer, pagesUntilFullRefresh);
 
   LOG_DBG("XTR", "Rendered page %lu/%lu (%u-bit)", currentPage + 1, xtc->getPageCount(), bitDepth);
 }

src/components/UITheme.cpp

@@ -13,10 +13,6 @@
 #include "components/themes/lyra/LyraTheme.h"
 #include "components/themes/roundedraff/RoundedRaffTheme.h"
 
-namespace {
-constexpr int SKIP_PAGE_MS = 700;
-}  // namespace
-
 UITheme UITheme::instance;
 
 UITheme::UITheme() {