fix: Scrolling page items calculation (#716)

## Summary

Fix for the page skip issue detected
https://github.com/crosspoint-reader/crosspoint-reader/pull/700#issuecomment-3856374323
by user @whyte-j

Skipping down on the last page now skips to the last item, and up on the
first page to the first item, rather than wrapping around the list in a
weird way.

## Additional Context

The calculation was outdated after several changes were added afterwards

---

### AI Usage

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please be transparent about their usage as it
helps set the right context for reviewers.

Did you use AI tools to help write this code? _**NO**_

src/activities/home/MyLibraryActivity.cpp

@@ -3,6 +3,8 @@
 #include <GfxRenderer.h>
 #include <SDCardManager.h>
 
+#include <algorithm>
+
 #include "MappedInputManager.h"
 #include "components/UITheme.h"
 #include "fontIds.h"
@@ -114,7 +116,7 @@ void MyLibraryActivity::loop() {
                             mappedInput.wasReleased(MappedInputManager::Button::Down);
 
   const bool skipPage = mappedInput.getHeldTime() > SKIP_PAGE_MS;
-  const int pageItems = UITheme::getInstance().getNumberOfItemsPerPage(renderer, true, false, true, true);
+  const int pageItems = UITheme::getInstance().getNumberOfItemsPerPage(renderer, true, false, true, false);
 
   if (mappedInput.wasReleased(MappedInputManager::Button::Confirm)) {
     if (files.empty()) {
@@ -157,14 +159,14 @@ void MyLibraryActivity::loop() {
   int listSize = static_cast<int>(files.size());
   if (upReleased) {
     if (skipPage) {
-      selectorIndex = ((selectorIndex / pageItems - 1) * pageItems + listSize) % listSize;
+      selectorIndex = std::max(static_cast<int>((selectorIndex / pageItems - 1) * pageItems), 0);
     } else {
       selectorIndex = (selectorIndex + listSize - 1) % listSize;
     }
     updateRequired = true;
   } else if (downReleased) {
     if (skipPage) {
-      selectorIndex = ((selectorIndex / pageItems + 1) * pageItems) % listSize;
+      selectorIndex = std::min(static_cast<int>((selectorIndex / pageItems + 1) * pageItems), listSize - 1);
     } else {
       selectorIndex = (selectorIndex + 1) % listSize;
     }
@@ -195,7 +197,7 @@ void MyLibraryActivity::render() const {
   GUI.drawHeader(renderer, Rect{0, metrics.topPadding, pageWidth, metrics.headerHeight}, folderName);
 
   const int contentTop = metrics.topPadding + metrics.headerHeight + metrics.verticalSpacing;
-  const int contentHeight = pageHeight - contentTop - metrics.buttonHintsHeight - metrics.verticalSpacing * 2;
+  const int contentHeight = pageHeight - contentTop - metrics.buttonHintsHeight - metrics.verticalSpacing;
   if (files.empty()) {
     renderer.drawText(UI_10_FONT_ID, metrics.contentSidePadding, contentTop + 20, "No books found");
   } else {

src/activities/home/RecentBooksActivity.cpp

@@ -3,6 +3,8 @@
 #include <GfxRenderer.h>
 #include <SDCardManager.h>
 
+#include <algorithm>
+
 #include "MappedInputManager.h"
 #include "RecentBooksStore.h"
 #include "components/UITheme.h"
@@ -92,14 +94,14 @@ void RecentBooksActivity::loop() {
   int listSize = static_cast<int>(recentBooks.size());
   if (upReleased) {
     if (skipPage) {
-      selectorIndex = ((selectorIndex / pageItems - 1) * pageItems + listSize) % listSize;
+      selectorIndex = std::max(static_cast<int>((selectorIndex / pageItems - 1) * pageItems), 0);
     } else {
       selectorIndex = (selectorIndex + listSize - 1) % listSize;
     }
     updateRequired = true;
   } else if (downReleased) {
     if (skipPage) {
-      selectorIndex = ((selectorIndex / pageItems + 1) * pageItems) % listSize;
+      selectorIndex = std::min(static_cast<int>((selectorIndex / pageItems + 1) * pageItems), listSize - 1);
     } else {
       selectorIndex = (selectorIndex + 1) % listSize;
     }
@@ -129,7 +131,7 @@ void RecentBooksActivity::render() const {
   GUI.drawHeader(renderer, Rect{0, metrics.topPadding, pageWidth, metrics.headerHeight}, "Recent Books");
 
   const int contentTop = metrics.topPadding + metrics.headerHeight + metrics.verticalSpacing;
-  const int contentHeight = pageHeight - contentTop - metrics.buttonHintsHeight - metrics.verticalSpacing * 2;
+  const int contentHeight = pageHeight - contentTop - metrics.buttonHintsHeight - metrics.verticalSpacing;
 
   // Recent tab
   if (recentBooks.empty()) {

src/components/UITheme.cpp

@@ -40,10 +40,10 @@ int UITheme::getNumberOfItemsPerPage(const GfxRenderer& renderer, bool hasHeader
   const ThemeMetrics& metrics = UITheme::getInstance().getMetrics();
   int reservedHeight = metrics.topPadding;
   if (hasHeader) {
-    reservedHeight += metrics.headerHeight;
+    reservedHeight += metrics.headerHeight + metrics.verticalSpacing;
   }
   if (hasTabBar) {
-    reservedHeight += metrics.tabBarHeight + metrics.verticalSpacing;
+    reservedHeight += metrics.tabBarHeight;
   }
   if (hasButtonHints) {
     reservedHeight += metrics.verticalSpacing + metrics.buttonHintsHeight;

src/components/themes/BaseTheme.cpp

@@ -174,7 +174,7 @@ void BaseTheme::drawList(const GfxRenderer& renderer, Rect rect, int itemCount,
 
     const int centerX = rect.x + rect.width - indicatorWidth / 2 - margin;
     const int indicatorTop = rect.y;  // Offset to avoid overlapping side button hints
-    const int indicatorBottom = rect.y + rect.height - 30;
+    const int indicatorBottom = rect.y + rect.height - arrowSize;
 
     // Draw up arrow at top (^) - narrow point at top, wide base at bottom
     for (int i = 0; i < arrowSize; ++i) {