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/ChatInput.tsx

@@ -0,0 +1,42 @@
+import { useState } from "react";
+import { Send } from "lucide-react";
+import { Button } from "@/routes/ui/button";
+
+interface ChatInputProps {
+    onSend: (content: string) => void;
+    disabled?: boolean;
+    placeholder?: string;
+}
+
+/**
+ * Chat input component with send button
+ */
+export function ChatInput({ onSend, disabled, placeholder }: ChatInputProps) {
+    const [input, setInput] = useState("");
+
+    const handleSubmit = (e: React.FormEvent) => {
+        e.preventDefault();
+        if (input.trim() && !disabled) {
+            onSend(input.trim());
+            setInput("");
+        }
+    };
+
+    return (
+        <form onSubmit={handleSubmit} className="border-t p-3">
+            <div className="flex gap-2">
+                <input
+                    type="text"
+                    value={input}
+                    onChange={(e) => setInput(e.target.value)}
+                    placeholder={placeholder || "Type a message..."}
+                    disabled={disabled}
+                    className="flex-1 px-3 py-2 border rounded-md bg-background text-sm focus:outline-none focus:ring-2 focus:ring-primary"
+                />
+                <Button type="submit" size="icon" disabled={disabled || !input.trim()}>
+                    <Send className="h-4 w-4" />
+                </Button>
+            </div>
+        </form>
+    );
+}