feat(browser): implement browser extension for sending files to DocuElevate

- Add complete browser extension with popup UI and background workers
- Support Chrome, Firefox, Edge, and other Chromium-based browsers
- Include context menu integration for quick file sending
- Add comprehensive documentation for users and administrators
- Update main README and API docs to include browser extension
- Implement secure configuration storage in browser extension storage
- Add SSRF-protected URL upload endpoint integration

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

browser-extension/scripts/content.js

@@ -0,0 +1,33 @@
+// Content script for DocuElevate browser extension
+
+// This script runs on all web pages to detect file URLs
+// and enable communication between page content and the extension
+
+// Listen for messages from the popup
+chrome.runtime.onMessage.addListener((message, sender, sendResponse) => {
+    if (message.type === 'GET_PAGE_INFO') {
+        // Return information about the current page
+        const pageInfo = {
+            url: window.location.href,
+            title: document.title
+        };
+        sendResponse(pageInfo);
+    }
+});
+
+// Detect if current page is a direct file link
+function isDirectFileUrl(url) {
+    const fileExtensions = [
+        '.pdf', '.doc', '.docx', '.xls', '.xlsx', '.ppt', '.pptx',
+        '.txt', '.csv', '.rtf', '.jpg', '.jpeg', '.png', '.gif',
+        '.bmp', '.tiff', '.webp', '.svg'
+    ];
+    
+    const urlLower = url.toLowerCase();
+    return fileExtensions.some(ext => urlLower.endsWith(ext));
+}
+
+// Add visual indicator for file pages (optional enhancement)
+if (isDirectFileUrl(window.location.href)) {
+    console.log('DocuElevate: Direct file URL detected');
+}