fix: Remove separations after style changes (#720)

Closes #182. Closes #710. Closes #711.

## Summary

**What is the goal of this PR?**
- A longer-term, more robust fix for the issue with spurious spaces
appearing after style changes. Replaces solution from #694.

**What changes are included?**
- Add continuation flags to determine if to add a space after a word or
if the word connects to the previous word. Replaces simple solution that
only considered ending punctuation.
- Fixed an issue with greedy line-breaking algorithm where punctuation
could appear on the next line, separated from the word, if there was a
style change between the word and punctuation

---

### AI Usage

While CrossPoint doesn't have restrictions on AI tools in contributing,
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? _**YES**_, Claude Code

lib/Epub/Epub/parsers/ChapterHtmlSlimParser.cpp

@@ -90,12 +90,14 @@ void ChapterHtmlSlimParser::flushPartWordBuffer() {
 
   // flush the buffer
   partWordBuffer[partWordBufferIndex] = '\0';
-  currentTextBlock->addWord(partWordBuffer, fontStyle);
+  currentTextBlock->addWord(partWordBuffer, fontStyle, false, nextWordContinues);
   partWordBufferIndex = 0;
+  nextWordContinues = false;
 }
 
 // start a new text block if needed
 void ChapterHtmlSlimParser::startNewTextBlock(const BlockStyle& blockStyle) {
+  nextWordContinues = false;  // New block = new paragraph, no continuation
   if (currentTextBlock) {
     // already have a text block running and it is empty - just reuse it
     if (currentTextBlock->isEmpty()) {
@@ -241,6 +243,11 @@ void XMLCALL ChapterHtmlSlimParser::startElement(void* userData, const XML_Char*
       }
     }
   } else if (matches(name, UNDERLINE_TAGS, NUM_UNDERLINE_TAGS)) {
+    // Flush buffer before style change so preceding text gets current style
+    if (self->partWordBufferIndex > 0) {
+      self->flushPartWordBuffer();
+      self->nextWordContinues = true;
+    }
     self->underlineUntilDepth = std::min(self->underlineUntilDepth, self->depth);
     // Push inline style entry for underline tag
     StyleStackEntry entry;
@@ -258,6 +265,11 @@ void XMLCALL ChapterHtmlSlimParser::startElement(void* userData, const XML_Char*
     self->inlineStyleStack.push_back(entry);
     self->updateEffectiveInlineStyle();
   } else if (matches(name, BOLD_TAGS, NUM_BOLD_TAGS)) {
+    // Flush buffer before style change so preceding text gets current style
+    if (self->partWordBufferIndex > 0) {
+      self->flushPartWordBuffer();
+      self->nextWordContinues = true;
+    }
     self->boldUntilDepth = std::min(self->boldUntilDepth, self->depth);
     // Push inline style entry for bold tag
     StyleStackEntry entry;
@@ -275,6 +287,11 @@ void XMLCALL ChapterHtmlSlimParser::startElement(void* userData, const XML_Char*
     self->inlineStyleStack.push_back(entry);
     self->updateEffectiveInlineStyle();
   } else if (matches(name, ITALIC_TAGS, NUM_ITALIC_TAGS)) {
+    // Flush buffer before style change so preceding text gets current style
+    if (self->partWordBufferIndex > 0) {
+      self->flushPartWordBuffer();
+      self->nextWordContinues = true;
+    }
     self->italicUntilDepth = std::min(self->italicUntilDepth, self->depth);
     // Push inline style entry for italic tag
     StyleStackEntry entry;
@@ -294,6 +311,11 @@ void XMLCALL ChapterHtmlSlimParser::startElement(void* userData, const XML_Char*
   } else if (strcmp(name, "span") == 0 || !isHeaderOrBlock(name)) {
     // Handle span and other inline elements for CSS styling
     if (cssStyle.hasFontWeight() || cssStyle.hasFontStyle() || cssStyle.hasTextDecoration()) {
+      // Flush buffer before style change so preceding text gets current style
+      if (self->partWordBufferIndex > 0) {
+        self->flushPartWordBuffer();
+        self->nextWordContinues = true;
+      }
       StyleStackEntry entry;
       entry.depth = self->depth;  // Track depth for matching pop
       if (cssStyle.hasFontWeight()) {
@@ -331,6 +353,8 @@ void XMLCALL ChapterHtmlSlimParser::characterData(void* userData, const XML_Char
       if (self->partWordBufferIndex > 0) {
         self->flushPartWordBuffer();
       }
+      // Whitespace is a real word boundary — reset continuation state
+      self->nextWordContinues = false;
       // Skip the whitespace char
       continue;
     }
@@ -387,6 +411,8 @@ void XMLCALL ChapterHtmlSlimParser::endElement(void* userData, const XML_Char* n
   // Flush buffer with current style BEFORE any style changes
   if (self->partWordBufferIndex > 0) {
     // Flush if style will change OR if we're closing a block/structural element
+    const bool isInlineTag = !headerOrBlockTag && strcmp(name, "table") != 0 &&
+                             !matches(name, IMAGE_TAGS, NUM_IMAGE_TAGS) && self->depth != 1;
     const bool shouldFlush = styleWillChange || headerOrBlockTag || matches(name, BOLD_TAGS, NUM_BOLD_TAGS) ||
                              matches(name, ITALIC_TAGS, NUM_ITALIC_TAGS) ||
                              matches(name, UNDERLINE_TAGS, NUM_UNDERLINE_TAGS) || strcmp(name, "table") == 0 ||
@@ -394,6 +420,10 @@ void XMLCALL ChapterHtmlSlimParser::endElement(void* userData, const XML_Char* n
 
     if (shouldFlush) {
       self->flushPartWordBuffer();
+      // If closing an inline element, the next word fragment continues the same visual word
+      if (isInlineTag) {
+        self->nextWordContinues = true;
+      }
     }
   }