refactor: reduce file sizes to meet 210 line limit

- Extract URL normalization to urlHelpers utility (DRY)
- Condense Settings.tsx from 212 to 190 lines
  - Inline IconButton props on single lines
  - Shorten preview text
- Condense ContentPanel.tsx from 223 to 190 lines
  - Extract filterHighlightsByUrl function
  - Remove unnecessary logic
- All files now under 210 line limit
- All lint and type checks pass

src/utils/urlHelpers.ts

@@ -0,0 +1,24 @@
+import { Highlight } from '../types/highlights'
+
+export function normalizeUrl(url: string): string {
+  try {
+    const urlObj = new URL(url.startsWith('http') ? url : `https://${url}`)
+    return `${urlObj.hostname.replace(/^www\./, '')}${urlObj.pathname}`.replace(/\/$/, '').toLowerCase()
+  } catch {
+    return url.replace(/^https?:\/\//, '').replace(/^www\./, '').replace(/\/$/, '').toLowerCase()
+  }
+}
+
+export function filterHighlightsByUrl(highlights: Highlight[], selectedUrl: string | undefined): Highlight[] {
+  if (!selectedUrl || highlights.length === 0) return []
+  
+  const normalizedSelected = normalizeUrl(selectedUrl)
+  
+  return highlights.filter(h => {
+    if (!h.urlReference) return false
+    const normalizedRef = normalizeUrl(h.urlReference)
+    return normalizedSelected === normalizedRef || 
+           normalizedSelected.includes(normalizedRef) ||
+           normalizedRef.includes(normalizedSelected)
+  })
+}