Fix mobile performance degradation during typing and after image upload

Memoize blob URL creation to prevent leak on every keystroke, wrap
MessageInput in React.memo with stable useCallback props, remove
expensive backdrop-blur-sm from chat footer, and use instant scroll
during streaming to avoid queuing smooth scroll animations.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

raggr-frontend/src/components/ChatScreen.tsx

@@ -1,4 +1,4 @@
-import { useEffect, useState, useRef } from "react";
+import { useCallback, useEffect, useState, useRef } from "react";
 import { LogOut, Shield, PanelLeftClose, PanelLeftOpen, Menu, X } from "lucide-react";
 import { conversationService } from "../api/conversationService";
 import { userService } from "../api/userService";
@@ -63,9 +63,13 @@ export const ChatScreen = ({ setAuthenticated }: ChatScreenProps) => {
   const abortControllerRef = useRef<AbortController | null>(null);
   const simbaAnswers = ["meow.", "hiss...", "purrrrrr", "yowOWROWWowowr"];
 
-  const scrollToBottom = () => {
-    messagesEndRef.current?.scrollIntoView({ behavior: "smooth" });
-  };
+  const scrollToBottom = useCallback(() => {
+    requestAnimationFrame(() => {
+      messagesEndRef.current?.scrollIntoView({
+        behavior: isLoading ? "instant" : "smooth",
+      });
+    });
+  }, [isLoading]);
 
   useEffect(() => {
     isMountedRef.current = true;
@@ -130,7 +134,7 @@ export const ChatScreen = ({ setAuthenticated }: ChatScreenProps) => {
     load();
   }, [selectedConversation?.id]);
 
-  const handleQuestionSubmit = async () => {
+  const handleQuestionSubmit = useCallback(async () => {
     if ((!query.trim() && !pendingImage) || isLoading) return;
 
     let activeConversation = selectedConversation;
@@ -214,19 +218,22 @@ export const ChatScreen = ({ setAuthenticated }: ChatScreenProps) => {
       if (isMountedRef.current) setIsLoading(false);
       abortControllerRef.current = null;
     }
-  };
+  }, [query, pendingImage, isLoading, selectedConversation, simbaMode, messages, setAuthenticated]);
 
-  const handleQueryChange = (event: React.ChangeEvent<HTMLTextAreaElement>) => {
+  const handleQueryChange = useCallback((event: React.ChangeEvent<HTMLTextAreaElement>) => {
     setQuery(event.target.value);
-  };
+  }, []);
 
-  const handleKeyDown = (event: React.ChangeEvent<HTMLTextAreaElement>) => {
+  const handleKeyDown = useCallback((event: React.ChangeEvent<HTMLTextAreaElement>) => {
     const kev = event as unknown as React.KeyboardEvent<HTMLTextAreaElement>;
     if (kev.key === "Enter" && !kev.shiftKey) {
       kev.preventDefault();
       handleQuestionSubmit();
     }
-  };
+  }, [handleQuestionSubmit]);
+
+  const handleImageSelect = useCallback((file: File) => setPendingImage(file), []);
+  const handleClearImage = useCallback(() => setPendingImage(null), []);
 
   const handleLogout = () => {
     localStorage.removeItem("access_token");
@@ -380,8 +387,8 @@ export const ChatScreen = ({ setAuthenticated }: ChatScreenProps) => {
                 setSimbaMode={setSimbaMode}
                 isLoading={isLoading}
                 pendingImage={pendingImage}
-                onImageSelect={(file) => setPendingImage(file)}
-                onClearImage={() => setPendingImage(null)}
+                onImageSelect={handleImageSelect}
+                onClearImage={handleClearImage}
               />
             </div>
           </div>
@@ -416,7 +423,7 @@ export const ChatScreen = ({ setAuthenticated }: ChatScreenProps) => {
               </div>
             </div>
 
-            <footer className="border-t border-sand-light/40 bg-cream/80 backdrop-blur-sm">
+            <footer className="border-t border-sand-light/40 bg-cream">
               <div className="max-w-2xl mx-auto px-4 py-3">
                 <MessageInput
                   query={query}