fix(webui): opaque composer, equal-width message area, cleaner user pill

webui/src/components/MessageBubble.tsx

@@ -42,9 +42,8 @@ export function MessageBubble({ message }: MessageBubbleProps) {
         {hasText ? (
           <p
             className={cn(
-              "ml-auto w-fit rounded-[18px] border border-border/60 bg-secondary/70 px-4 py-2",
+              "ml-auto w-fit rounded-[18px] bg-secondary/70 px-4 py-2",
               "text-left text-[18px]/[1.8] whitespace-pre-wrap break-words",
-              "shadow-[0_10px_24px_-18px_rgba(0,0,0,0.55)]",
             )}
           >
             {message.content}

webui/src/components/thread/ThreadComposer.tsx

@@ -216,9 +216,9 @@ export function ThreadComposer({
         className={cn(
           "relative mx-auto flex w-full flex-col overflow-hidden transition-all duration-200",
           isHero
-            ? "max-w-[40rem] rounded-[24px] border border-border/75 bg-card/72 shadow-[0_10px_30px_rgba(0,0,0,0.10)]"
-            : "max-w-[49.5rem] rounded-[16px] border border-border/70 bg-card/55",
-          "focus-within:bg-card/70 focus-within:ring-1 focus-within:ring-foreground/8",
+            ? "max-w-[40rem] rounded-[24px] border border-border/75 bg-card shadow-[0_10px_30px_rgba(0,0,0,0.10)]"
+            : "max-w-[49.5rem] rounded-[16px] border border-border/70 bg-card",
+          "focus-within:ring-1 focus-within:ring-foreground/8",
           disabled && "opacity-60",
           isDragging && "ring-2 ring-primary/40 motion-reduce:ring-0 motion-reduce:border-primary",
         )}

webui/src/components/thread/ThreadViewport.tsx

@@ -70,10 +70,12 @@ export function ThreadViewport({
         {hasMessages ? (
           <div className="mx-auto flex min-h-full w-full max-w-[64rem] flex-col">
             <div className="flex-1 px-4 pb-20 pt-4">
-              <ThreadMessages messages={messages} />
+              <div className="mx-auto w-full max-w-[49.5rem]">
+                <ThreadMessages messages={messages} />
+              </div>
             </div>
 
-            <div className="sticky bottom-0 z-10 mt-auto">
+            <div className="sticky bottom-0 z-10 mt-auto bg-background">
               <div className="px-4 pb-3">
                 {composer}
               </div>