fix React 19 infinite re-render loop on live dashboard

The "Maximum update depth exceeded" error was caused by two issues:

1. useDeferredStreamMetadata returned a new `{}` default on every render
   when SWR data was undefined, creating an unstable reference that
   triggered the useEffect in useCameraLiveMode on every render cycle.
   Fixed by using a stable module-level EMPTY_METADATA constant.

2. useResizeObserver's rest parameter `...refs` created a new array on
   every render, causing its useEffect to re-run and re-observe elements
   continuously. Fixed by stabilizing refs with useRef and only
   reconnecting the observer when actual DOM elements change.

web/src/hooks/resize-observer.ts

@@ -1,4 +1,4 @@
-import { MutableRefObject, useEffect, useMemo, useState } from "react";
+import { MutableRefObject, useEffect, useMemo, useRef, useState } from "react";
 
 type RefType = MutableRefObject<Element | null> | Window;
 
@@ -31,25 +31,39 @@ export function useResizeObserver(...refs: RefType[]) {
     [],
   );
 
+  // Stabilize refs array to prevent useEffect from re-running on every render
+  // (rest params create a new array each call)
+  const stableRefs = useRef(refs);
+  stableRefs.current = refs;
+
+  // Track observed elements to detect actual changes
+  const observedElements = useRef<(Element | null)[]>([]);
+
   useEffect(() => {
-    refs.forEach((ref) => {
-      if (ref instanceof Window) {
-        resizeObserver.observe(document.body);
-      } else if (ref.current) {
-        resizeObserver.observe(ref.current);
-      }
+    const currentRefs = stableRefs.current;
+    const elements = currentRefs.map((ref) =>
+      ref instanceof Window ? document.body : ref.current,
+    );
+
+    // Only re-observe if actual DOM elements changed
+    const prevElements = observedElements.current;
+    const changed =
+      elements.length !== prevElements.length ||
+      elements.some((el, i) => el !== prevElements[i]);
+
+    if (!changed) return;
+
+    // Disconnect all and re-observe
+    resizeObserver.disconnect();
+    elements.forEach((el) => {
+      if (el) resizeObserver.observe(el);
     });
+    observedElements.current = elements;
 
     return () => {
-      refs.forEach((ref) => {
-        if (ref instanceof Window) {
-          resizeObserver.unobserve(document.body);
-        } else if (ref.current) {
-          resizeObserver.unobserve(ref.current);
-        }
-      });
+      resizeObserver.disconnect();
     };
-  }, [refs, resizeObserver]);
+  });
 
   if (dimensions.length == refs.length) {
     return dimensions;

web/src/hooks/use-deferred-stream-metadata.ts

@@ -5,6 +5,7 @@ import { LiveStreamMetadata } from "@/types/live";
 
 const FETCH_TIMEOUT_MS = 10000;
 const DEFER_DELAY_MS = 2000;
+const EMPTY_METADATA: { [key: string]: LiveStreamMetadata } = {};
 
 /**
  * Hook that fetches go2rtc stream metadata with deferred loading.
@@ -77,7 +78,7 @@ export default function useDeferredStreamMetadata(streamNames: string[]) {
     return metadata;
   }, []);
 
-  const { data: metadata = {} } = useSWR<{
+  const { data: metadata = EMPTY_METADATA } = useSWR<{
     [key: string]: LiveStreamMetadata;
   }>(swrKey, fetcher, {
     revalidateOnFocus: false,