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/textMatching.ts

@@ -0,0 +1,46 @@
+import { Highlight } from '../../types/highlights'
+
+export interface HighlightMatch {
+  highlight: Highlight
+  startIndex: number
+  endIndex: number
+}
+
+/**
+ * Normalize whitespace for flexible matching
+ */
+export const normalizeWhitespace = (str: string) => str.replace(/\s+/g, ' ').trim()
+
+/**
+ * Find all occurrences of highlight text in the content
+ */
+export function findHighlightMatches(
+  content: string,
+  highlights: Highlight[]
+): HighlightMatch[] {
+  const matches: HighlightMatch[] = []
+  
+  for (const highlight of highlights) {
+    if (!highlight.content || highlight.content.trim().length === 0) {
+      continue
+    }
+    
+    const searchText = highlight.content.trim()
+    let startIndex = 0
+    
+    let index = content.indexOf(searchText, startIndex)
+    while (index !== -1) {
+      matches.push({
+        highlight,
+        startIndex: index,
+        endIndex: index + searchText.length
+      })
+      
+      startIndex = index + searchText.length
+      index = content.indexOf(searchText, startIndex)
+    }
+  }
+  
+  return matches.sort((a, b) => a.startIndex - b.startIndex)
+}
+