refactor(highlights): split highlighting utilities into modules

- Create textMatching module for text search utilities
- Create domUtils module for DOM manipulation helpers
- Create htmlMatching module for HTML highlight application
- Reduce highlightMatching.tsx from 217 lines to 59 lines
- All files now under 210 lines

src/utils/highlightMatching/htmlMatching.ts

@@ -0,0 +1,60 @@
+import { Highlight } from '../../types/highlights'
+import { tryMarkInTextNodes } from './domUtils'
+
+/**
+ * Apply highlights to HTML content by injecting mark tags using DOM manipulation
+ */
+export function applyHighlightsToHTML(
+  html: string, 
+  highlights: Highlight[], 
+  highlightStyle: 'marker' | 'underline' = 'marker'
+): string {
+  if (!html || highlights.length === 0) {
+    console.log('⚠️ applyHighlightsToHTML: No HTML or highlights', { 
+      htmlLength: html?.length, 
+      highlightsCount: highlights.length 
+    })
+    return html
+  }
+  
+  console.log('🔨 applyHighlightsToHTML: Processing', highlights.length, 'highlights')
+  
+  const tempDiv = document.createElement('div')
+  tempDiv.innerHTML = html
+  
+  let appliedCount = 0
+  
+  for (const highlight of highlights) {
+    const searchText = highlight.content.trim()
+    if (!searchText) {
+      console.warn('⚠️ Empty highlight content:', highlight.id)
+      continue
+    }
+    
+    console.log('🔍 Searching for highlight:', searchText.substring(0, 50) + '...')
+    
+    // Collect all text nodes
+    const walker = document.createTreeWalker(tempDiv, NodeFilter.SHOW_TEXT, null)
+    const textNodes: Text[] = []
+    let node: Node | null
+    while ((node = walker.nextNode())) textNodes.push(node as Text)
+    
+    console.log('📄 Found', textNodes.length, 'text nodes to search')
+    
+    // Try exact match first, then normalized match
+    const found = tryMarkInTextNodes(textNodes, searchText, highlight, false, highlightStyle) ||
+                  tryMarkInTextNodes(textNodes, searchText, highlight, true, highlightStyle)
+    
+    if (found) {
+      appliedCount++
+      console.log('✅ Highlight applied successfully')
+    } else {
+      console.warn('❌ Could not find match for highlight:', searchText.substring(0, 50))
+    }
+  }
+  
+  console.log('🎉 Applied', appliedCount, '/', highlights.length, 'highlights')
+  
+  return tempDiv.innerHTML
+}
+