feat: allow network admin to control ephemerality setting

Resolves #92

js/src/hooks/use-stream-playback.ts

@@ -2,10 +2,10 @@ import { useCallback, useEffect, useEffectEvent, useMemo, useReducer, useRef, us
 import { useAuthStore } from "@/stores/auth-store";
 import type { Particle } from "@/api/types";
 import { useLiveParticleChildren } from "@/hooks/use-particle";
-import { toFirestoreDocPath, type ParticlePath } from "@/lib/particle-path";
+import { parseParticlePath, toFirestoreDocPath, type ParticlePath } from "@/lib/particle-path";
 import { updateStreamPlaybackMarker } from "@/lib/firestore-particles";
 import { where, Timestamp } from "firebase/firestore";
-import { RECENCY_WINDOW_HOURS } from "@/lib/constants";
+import { useNetwork } from "@/hooks/use-networks";
 
 // --- Playback reducer (ID-based) ---
 
@@ -96,6 +96,9 @@ export function useStreamPlayback(
   path: ParticlePath,
 ): UseStreamPlaybackResult {
   const userId = useAuthStore((s) => s.user?.id);
+  const { networkId } = parseParticlePath(path);
+  const network = useNetwork(networkId);
+  const retentionHours = network?.message_retention_hours ?? 24;
   const [state, dispatch] = useReducer(playbackReducer, initialState);
   // Track the stream ID we've initialized for, to reset when navigating between streams
   const initializedForRef = useRef<string | null>(null);
@@ -117,7 +120,7 @@ export function useStreamPlayback(
 
   const [recencyCutoff] = useState(() => {
     const d = new Date();
-    d.setHours(d.getHours() - RECENCY_WINDOW_HOURS);
+    d.setHours(d.getHours() - retentionHours);
     return Timestamp.fromDate(d);
   });