feat: User setting for image display (#1291)

## Summary

**What is the goal of this PR?** Add a user setting to decide image
support: display, show placeholder instead, supress fully

Fixes #1289

---

### AI Usage

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please be transparent about their usage as it
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Did you use AI tools to help write this code? _**< NO >**_

lib/Epub/Epub/parsers/ChapterHtmlSlimParser.cpp

@@ -243,7 +243,14 @@ void XMLCALL ChapterHtmlSlimParser::startElement(void* userData, const XML_Char*
         }
       }
 
-      if (!src.empty()) {
+      // imageRendering: 0=display, 1=placeholder (alt text only), 2=suppress entirely
+      if (self->imageRendering == 2) {
+        self->skipUntilDepth = self->depth;
+        self->depth += 1;
+        return;
+      }
+
+      if (!src.empty() && self->imageRendering != 1) {
         LOG_DBG("EHP", "Found image: src=%s", src.c_str());
 
         {

lib/Epub/Epub/parsers/ChapterHtmlSlimParser.h

@@ -48,6 +48,7 @@ class ChapterHtmlSlimParser {
   bool hyphenationEnabled;
   const CssParser* cssParser;
   bool embeddedStyle;
+  uint8_t imageRendering;
   std::string contentBase;
   std::string imageBasePath;
   int imageCounter = 0;
@@ -94,8 +95,8 @@ class ChapterHtmlSlimParser {
                                  const uint16_t viewportHeight, const bool hyphenationEnabled,
                                  const std::function<void(std::unique_ptr<Page>)>& completePageFn,
                                  const bool embeddedStyle, const std::string& contentBase,
-                                 const std::string& imageBasePath, const std::function<void()>& popupFn = nullptr,
-                                 const CssParser* cssParser = nullptr)
+                                 const std::string& imageBasePath, const uint8_t imageRendering = 0,
+                                 const std::function<void()>& popupFn = nullptr, const CssParser* cssParser = nullptr)
 
       : epub(epub),
         filepath(filepath),
@@ -111,6 +112,7 @@ class ChapterHtmlSlimParser {
         popupFn(popupFn),
         cssParser(cssParser),
         embeddedStyle(embeddedStyle),
+        imageRendering(imageRendering),
         contentBase(contentBase),
         imageBasePath(imageBasePath) {}