Add dice-roll animation and tighten attack-roll prompt rules

Broadcast a "rolling" WS event when the DM invokes roll_dice, and show
a cycling dice-emoji animation with the roll notation in the chat while
waiting for the result, instead of just the generic typing indicator.

Also split the dice-roll prompt rule into skill/save checks (DC shown
to the player) vs. attack rolls (AC stays secret but must still be
labeled as a roll), and made the "always roll yourself, never ask the
player to roll" instruction unconditional.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/pages/GameSession.tsx

@@ -20,6 +20,7 @@ export default function GameSession() {
   const [selectedCharacterId, setSelectedCharacterId] = useState("");
   const [joinError, setJoinError] = useState<string | null>(null);
   const [isTyping, setIsTyping] = useState(false);
+  const [rollingNotation, setRollingNotation] = useState<string | null>(null);
 
   async function loadGame() {
     if (!gameId) return;
@@ -71,6 +72,7 @@ export default function GameSession() {
     game?.is_participant ? gameId : undefined,
     (incoming) => {
       setIsTyping(false);
+      setRollingNotation(null);
       setMessages((prev) => {
         const next = [...prev, incoming];
         return showingFull ? next : next.slice(-5);
@@ -78,6 +80,7 @@ export default function GameSession() {
     },
     (detail) => {
       setIsTyping(false);
+      setRollingNotation(null);
       const text =
         detail === "connection_lost"
           ? "Verbindung zum Server verloren. Bitte lade die Seite neu."
@@ -98,6 +101,7 @@ export default function GameSession() {
       });
     },
     () => setIsTyping(true),
+    (notation) => setRollingNotation(notation),
   );
 
   async function handleSend(content: string) {
@@ -177,7 +181,7 @@ export default function GameSession() {
       </div>
 
       <div className="flex flex-1 flex-col overflow-hidden rounded-lg border border-slate-800 bg-slate-900">
-        <TranscriptPane messages={messages} typing={isTyping} />
+        <TranscriptPane messages={messages} typing={isTyping} rolling={rollingNotation} />
         <SendMessageForm onSend={handleSend} />
       </div>
     </div>