feat(group-chat): add ephemeral visual pass indicator when bot passes turn

- Display a subtle centered system pill '[⏩ {bot} passed]' when a bot passes
- Style with Material icon (Icons.Filled.FastForward) and surface tokens
- Keep pass indicators strictly ephemeral to avoid polluting LLM prompt context
- Exclude from cross-device snapshot sync so it disappears on restart/rehydrate
- Add English and Arabic localized string resources
- Update GroupChatViewModelTest to verify pass indicator presence and LLM filtering

Co-authored-by: Luna <luna.m57@agentmail.to>

app/src/main/res/values/strings.xml

@@ -1283,6 +1283,7 @@
     <string name="group_chat_empty_title">No Messages Yet</string>
     <string name="group_chat_empty_subtitle">Mention a bot or use @all to kick off collaboration.</string>
     <string name="group_chat_thinking">%1$s is thinking…</string>
+    <string name="group_chat_bot_passed">%1$s passed</string>
     <string name="group_chat_typing">Typing…</string>
     <string name="group_chat_tool_running">Running…</string>
     <string name="group_chat_tool_no_output">No output</string>