fix: Re-apply upstream PRs #1005, #1010, #1003

Re-applies changes that were accidentally discarded during a prior
dry-run cherry-pick reset (git checkout -- .).

- PR #1005: Use HalPowerManager for battery percentage (uint16_t return
  type, remove Battery.h, update theme files)
- PR #1010: Fix dangling pointer in onGoToReader()
- PR #1003: Render image placeholders while waiting for decode (adds
  isCached, renderPlaceholder, renderTextOnly, countUncachedImages,
  renderImagePlaceholders)

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/Epub/Epub/Page.cpp

@@ -61,6 +61,49 @@ std::unique_ptr<PageImage> PageImage::deserialize(FsFile& file) {
   return std::unique_ptr<PageImage>(new PageImage(std::move(ib), xPos, yPos));
 }
 
+bool PageImage::isCached() const { return imageBlock->isCached(); }
+
+void PageImage::renderPlaceholder(GfxRenderer& renderer, const int xOffset, const int yOffset) const {
+  int x = xPos + xOffset;
+  int y = yPos + yOffset;
+  int w = imageBlock->getWidth();
+  int h = imageBlock->getHeight();
+  renderer.fillRect(x, y, w, h, true);
+  if (w > 2 && h > 2) {
+    renderer.fillRect(x + 1, y + 1, w - 2, h - 2, false);
+  }
+}
+
+void Page::renderTextOnly(GfxRenderer& renderer, const int fontId, const int xOffset, const int yOffset) const {
+  for (auto& element : elements) {
+    if (element->getTag() == TAG_PageLine) {
+      element->render(renderer, fontId, xOffset, yOffset);
+    }
+  }
+}
+
+int Page::countUncachedImages() const {
+  int count = 0;
+  for (auto& element : elements) {
+    if (element->getTag() == TAG_PageImage) {
+      auto* img = static_cast<PageImage*>(element.get());
+      if (!img->isCached()) {
+        count++;
+      }
+    }
+  }
+  return count;
+}
+
+void Page::renderImagePlaceholders(GfxRenderer& renderer, const int xOffset, const int yOffset) const {
+  for (auto& element : elements) {
+    if (element->getTag() == TAG_PageImage) {
+      auto* img = static_cast<PageImage*>(element.get());
+      img->renderPlaceholder(renderer, xOffset, yOffset);
+    }
+  }
+}
+
 // ---------------------------------------------------------------------------
 // PageTableRow
 // ---------------------------------------------------------------------------

lib/Epub/Epub/Page.h

@@ -80,6 +80,8 @@ class PageImage final : public PageElement {
   void render(GfxRenderer& renderer, int fontId, int xOffset, int yOffset) override;
   bool serialize(FsFile& file) override;
   PageElementTag getTag() const override { return TAG_PageImage; }
+  bool isCached() const;
+  void renderPlaceholder(GfxRenderer& renderer, int xOffset, int yOffset) const;
   static std::unique_ptr<PageImage> deserialize(FsFile& file);
 
   // Helper to get image block dimensions (needed for bounding box calculation)
@@ -104,4 +106,8 @@ class Page {
   // Returns true if page has images and fills out the bounding box coordinates.
   // If no images, returns false.
   bool getImageBoundingBox(int& outX, int& outY, int& outWidth, int& outHeight) const;
+
+  void renderTextOnly(GfxRenderer& renderer, int fontId, int xOffset, int yOffset) const;
+  int countUncachedImages() const;
+  void renderImagePlaceholders(GfxRenderer& renderer, int xOffset, int yOffset) const;
 };

lib/Epub/Epub/blocks/ImageBlock.cpp

@@ -93,6 +93,11 @@ bool renderFromCache(GfxRenderer& renderer, const std::string& cachePath, int x,
 
 }  // namespace
 
+bool ImageBlock::isCached() const {
+  std::string cachePath = getCachePath(imagePath);
+  return Storage.exists(cachePath.c_str());
+}
+
 void ImageBlock::render(GfxRenderer& renderer, const int x, const int y) {
   LOG_DBG("IMG", "Rendering image at %d,%d: %s (%dx%d)", x, y, imagePath.c_str(), width, height);
 

lib/Epub/Epub/blocks/ImageBlock.h

@@ -16,6 +16,7 @@ class ImageBlock final : public Block {
   int16_t getHeight() const { return height; }
 
   bool imageExists() const;
+  bool isCached() const;
 
   BlockType getType() override { return IMAGE_BLOCK; }
   bool isEmpty() override { return false; }

lib/hal/HalPowerManager.cpp

@@ -78,7 +78,7 @@ void HalPowerManager::startDeepSleep(HalGPIO& gpio) const {
   esp_deep_sleep_start();
 }
 
-int HalPowerManager::getBatteryPercentage() const {
+uint16_t HalPowerManager::getBatteryPercentage() const {
   static const BatteryMonitor battery = BatteryMonitor(BAT_GPIO0);
   return battery.readPercentage();
 }

lib/hal/HalPowerManager.h

@@ -28,7 +28,7 @@ class HalPowerManager {
   void startDeepSleep(HalGPIO& gpio) const;
 
   // Get battery percentage (range 0-100)
-  int getBatteryPercentage() const;
+  uint16_t getBatteryPercentage() const;
 
   // RAII lock to prevent low-power mode during critical work (e.g. rendering)
   class Lock {