fix(ui): backoff remote-relay reconnects + stop cryptpad icon 404

Two console-noise fixes from a live error dump:
- remote-relay.ts reconnected on a FIXED 5s interval with no backoff, so when
  the backend is briefly down it floods the console/network with failed-WS
  attempts for the whole outage. It's a secondary feature (companion input), so
  add exponential backoff 1s->30s (mirrors websocket.ts), reset on open/start.
- cryptpad's catalog/marketplace entries pointed at a non-existent
  /assets/img/app-icons/cryptpad.webp -> a 404 on every marketplace render.
  Point it at the existing default icon (handleImageError swapped to it anyway).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

neode-ui/src/api/remote-relay.ts

@@ -38,6 +38,13 @@ export const companionInputActive = ref(false)
 let ws: WebSocket | null = null
 let shouldReconnect = true
 let reconnectTimer: ReturnType<typeof setTimeout> | null = null
+// Exponential backoff for the relay socket. It's a secondary feature (companion
+// input), so when the backend is down it must NOT hammer a fixed-interval
+// reconnect — that floods the console/network with failed-WS noise for the whole
+// outage. Back off 1s → 30s, reset on a successful open. (Mirrors websocket.ts.)
+let relayReconnectAttempts = 0
+const RELAY_RECONNECT_BASE_MS = 1000
+const RELAY_RECONNECT_MAX_MS = 30_000
 let cursorEl: HTMLDivElement | null = null
 let companionTimeout: ReturnType<typeof setTimeout> | null = null
 let inputFlickerTimeout: ReturnType<typeof setTimeout> | null = null
@@ -332,6 +339,7 @@ function doConnect() {
 
   ws.onopen = () => {
     relayConnected.value = true
+    relayReconnectAttempts = 0 // healthy again — reset backoff
     if (import.meta.env.DEV) console.log('[RemoteRelay] Connected')
   }
 
@@ -343,7 +351,12 @@ function doConnect() {
     relayConnected.value = false
     ws = null
     if (shouldReconnect) {
-      reconnectTimer = setTimeout(doConnect, 5000)
+      const delay = Math.min(
+        RELAY_RECONNECT_BASE_MS * 2 ** relayReconnectAttempts,
+        RELAY_RECONNECT_MAX_MS,
+      )
+      relayReconnectAttempts++
+      reconnectTimer = setTimeout(doConnect, delay)
     }
   }
 
@@ -379,6 +392,7 @@ export function requestExternalOpen(url: string): boolean {
 /** Start the remote relay listener. Connects to /ws/remote-relay. */
 export function startRemoteRelay() {
   shouldReconnect = true
+  relayReconnectAttempts = 0
   doConnect()
 }