fix: address code review feedback for browser extension

- Removed unused variables in capture.js (clonedDoc, styles array)
- Added explicit return values for message handlers in content.js
- Added detailed comment explaining 500ms render delay before PDF conversion
- Updated PERMISSIONS.md with comprehensive explanation of host_permissions requirement
- Updated test.html with web clipping test scenarios
- Improved code consistency and documentation

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

browser-extension/scripts/background.js

@@ -152,7 +152,9 @@ async function convertHtmlToPdf(html) {
             chrome.tabs.onUpdated.addListener(listener);
         });
         
-        // Give it a bit more time to render
+        // Wait for page to fully render before PDF conversion
+        // This delay ensures JavaScript execution, dynamic content rendering,
+        // and CSS transitions have completed. May need adjustment for complex pages.
         await new Promise(resolve => setTimeout(resolve, 500));
         
         // Use Chrome's print to PDF API