docs: update PRD with comprehensive extension features and UX integration strategy

- Added UX strategy: Extension for Quick Actions, Frontend for Management
- Organized features into 4 phases (Phase 1 completed)
- Added 14 new extension features (FR-EXT-07 to FR-EXT-17):
  * Smart Monitoring: Price alerts, whale tracking, rug pull detection
  * Trading Intelligence: Token analysis, entry/exit suggestions, portfolio tracker
  * Content Creation: Chart screenshots, AI thread generator
  * Productivity: Quick actions, notifications, keyboard shortcuts
- Added Feature Responsibility Matrix showing Extension vs Frontend roles
- Added Settings Sync strategy (FR-EXT-06) with deep links to frontend
- Documented state sync architecture: Extension ↔ Backend API ↔ Frontend

surfsense_browser_extension/sidepanel/chat/QuickCapture.tsx

@@ -0,0 +1,49 @@
+import { Camera } from "lucide-react";
+import { Button } from "@/routes/ui/button";
+import { useToast } from "@/routes/ui/use-toast";
+
+/**
+ * Quick capture button (sticky at bottom)
+ * Reuses existing capture functionality
+ */
+export function QuickCapture() {
+    const { toast } = useToast();
+
+    const handleCapture = async () => {
+        try {
+            // Get active tab
+            const [tab] = await chrome.tabs.query({ active: true, currentWindow: true });
+
+            if (!tab.id) {
+                throw new Error("No active tab");
+            }
+
+            // Send message to background to capture page
+            chrome.runtime.sendMessage({
+                type: "CAPTURE_PAGE",
+                tabId: tab.id,
+            });
+
+            toast({
+                title: "Page captured!",
+                description: "Saved to your search space",
+            });
+        } catch (error) {
+            console.error("Failed to capture page:", error);
+            toast({
+                title: "Capture failed",
+                description: "Please try again",
+                variant: "destructive",
+            });
+        }
+    };
+
+    return (
+        <div className="sticky bottom-0 border-t p-3 bg-background">
+            <Button className="w-full" onClick={handleCapture}>
+                <Camera className="mr-2 h-4 w-4" />
+                Save Current Page
+            </Button>
+        </div>
+    );
+}