feat(extension): add Firefox browser extension and native integration

- Implement Firefox extension to intercept downloads and scrape selected links via context menus
- Create LocalExtensionServer over TCP (localhost:6412) to receive links from the extension
- Automatically package extension to firelink.xpi in create_app_bundle.sh
- Add Integrations tab in SettingsView with one-click installer for Firefox variants
- Modify ContentView and TrayMenuView to automatically open the Add Downloads window on extension trigger

Extensions/Firefox/content.js

@@ -0,0 +1,37 @@
+// content.js
+chrome.runtime.onMessage.addListener((request, sender, sendResponse) => {
+  if (request.action === "extractSelectionLinks") {
+    const selection = window.getSelection();
+    if (!selection || selection.rangeCount === 0) {
+      sendResponse({ links: [] });
+      return;
+    }
+
+    const links = new Set();
+    
+    // Extract a tags from the selected range
+    for (let i = 0; i < selection.rangeCount; i++) {
+      const range = selection.getRangeAt(i);
+      const container = document.createElement("div");
+      container.appendChild(range.cloneContents());
+      
+      const anchors = container.querySelectorAll("a");
+      anchors.forEach(a => {
+        if (a.href) {
+          // ensure the link is a full URL by using the current document's base URI if it's relative
+          try {
+            const url = new URL(a.getAttribute('href'), document.baseURI).href;
+            links.add(url);
+          } catch (e) {
+            // Invalid URL, fallback to just checking if it looks like a valid protocol
+            if (a.href.startsWith("http")) {
+              links.add(a.href);
+            }
+          }
+        }
+      });
+    }
+
+    sendResponse({ links: Array.from(links) });
+  }
+});