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>

backend/app/llm/orchestrator.py

@@ -1,6 +1,7 @@
 import json
 import logging
 import uuid
+from collections.abc import Awaitable, Callable
 
 from sqlalchemy.ext.asyncio import AsyncSession
 
@@ -42,7 +43,10 @@ async def _execute_tool_call(
 
 
 async def run_dm_turn(
-    session: AsyncSession, game_id: uuid.UUID, latest_player_message: str | None = None
+    session: AsyncSession,
+    game_id: uuid.UUID,
+    latest_player_message: str | None = None,
+    on_roll: Callable[[str], Awaitable[None]] | None = None,
 ) -> Message:
     client = get_llm_client()
     system_prompt = get_dm_system_prompt()
@@ -83,6 +87,8 @@ async def run_dm_turn(
 
         for tool_call in message.tool_calls:
             tool_input = fix_double_escaped_unicode(json.loads(tool_call.function.arguments))
+            if tool_call.function.name == "roll_dice" and on_roll is not None:
+                await on_roll(tool_input.get("notation", ""))
             result = await _execute_tool_call(session, game_id, tool_call.function.name, tool_input)
             messages.append(
                 {