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>

src/activities/home/HomeActivity.cpp

@@ -13,7 +13,6 @@
 #include <cstring>
 #include <vector>
 
-#include "Battery.h"
 #include "CrossPointSettings.h"
 #include "CrossPointState.h"
 #include "MappedInputManager.h"

src/activities/reader/EpubReaderActivity.cpp

@@ -1020,6 +1020,14 @@ void EpubReaderActivity::renderContents(std::unique_ptr<Page> page, const int or
   // Force special handling for pages with images when anti-aliasing is on
   bool imagePageWithAA = page->hasImages() && SETTINGS.textAntiAliasing;
 
+  if (page->countUncachedImages() > 0) {
+    page->renderTextOnly(renderer, SETTINGS.getReaderFontId(), orientedMarginLeft, orientedMarginTop);
+    page->renderImagePlaceholders(renderer, orientedMarginLeft, orientedMarginTop);
+    renderStatusBar(orientedMarginRight, orientedMarginBottom, orientedMarginLeft);
+    renderer.displayBuffer();
+    renderer.clearScreen();
+  }
+
   page->render(renderer, SETTINGS.getReaderFontId(), orientedMarginLeft, orientedMarginTop);
 
   // Draw bookmark ribbon indicator in top-right corner if current page is bookmarked