feat(mobile): add huddles with LiveKit

Mirrors the desktop huddle window: tap the headphones button on a stream
to fetch a LiveKit token from Orion and join a video room. Active huddles
show a red badge on the stream card (participant count) and a red Join
pill in the stream top bar — both driven by huddle_active_participants
synced from the LiveKit webhook.

The HuddleScreen lives at its own route (not a modal/window): video tile
grid with placeholders for camera-off, mic/camera toggles, and a leave
button. Adds the LiveKit RN SDK plus the WebRTC + LiveKit Expo config
plugins for prebuild.

https://claude.ai/code/session_01Po5tAD17MXhnqGQ9hKh6PC

js/mobile/src/features/stream-view/StreamTopActions.tsx

@@ -1,9 +1,16 @@
-import { Pressable, Text, View } from "react-native";
-import { EllipsisVertical, Globe, Maximize2, Minimize2 } from "lucide-react-native";
+import { ActivityIndicator, Pressable, Text, View } from "react-native";
+import {
+  EllipsisVertical,
+  Globe,
+  Headphones,
+  Maximize2,
+  Minimize2,
+} from "lucide-react-native";
 import type { Human, Particle } from "@/api/types";
 import { parseVisibleTo } from "@/lib/stream-visibility";
 import { cn } from "@/lib/utils";
 import { Avatar } from "@/components/Avatar";
+import { useOpenHuddle } from "@/features/huddle/use-open-huddle";
 import { useStreamPresence } from "./stream-presence-context";
 
 interface StreamTopActionsProps {
@@ -36,6 +43,9 @@ export function StreamTopActions({
   showFitToggle,
 }: StreamTopActionsProps) {
   const { onlineHumanIds } = useStreamPresence();
+  const { open: openHuddle, loading: huddleLoading } = useOpenHuddle();
+  const huddleCount = streamParticle.huddle_active_participants?.length ?? 0;
+  const huddleActive = huddleCount > 0;
   const visibility = parseVisibleTo(streamParticle.visible_to, networkId);
   const memberIds =
     visibility.mode === "network"
@@ -79,6 +89,37 @@ export function StreamTopActions({
         ) : null}
       </Pressable>
 
+      <Pressable
+        onPress={() =>
+          void openHuddle(
+            networkId,
+            streamParticle.id,
+            streamParticle.properties.name,
+          )
+        }
+        disabled={huddleLoading}
+        accessibilityLabel={huddleActive ? "Join huddle" : "Start huddle"}
+        className={cn(
+          "h-8 items-center justify-center rounded-full px-2.5 flex-row gap-1",
+          huddleActive
+            ? "bg-red-500/90 active:bg-red-600"
+            : "bg-white/10 active:bg-white/20",
+        )}
+      >
+        {huddleLoading ? (
+          <ActivityIndicator color="white" size="small" />
+        ) : (
+          <>
+            <Headphones color="white" size={14} strokeWidth={2} />
+            {huddleActive ? (
+              <Text className="text-white text-xs font-semibold">
+                {huddleCount}
+              </Text>
+            ) : null}
+          </>
+        )}
+      </Pressable>
+
       {showFitToggle ? (
         <Pressable
           onPress={onToggleVideoFit}