Simplify and optimize notifications

src/app/components/MenuSpaceRoomItem.svelte

@@ -1,11 +1,10 @@
 <script lang="ts">
-  import {readable} from "svelte/store"
   import Icon from "@lib/components/Icon.svelte"
   import SecondaryNavItem from "@lib/components/SecondaryNavItem.svelte"
   import ChannelName from "@app/components/ChannelName.svelte"
   import {makeSpacePath} from "@app/routes"
   import {deriveChannel, channelIsLocked} from "@app/state"
-  import {deriveNotification, getRoomFilters} from "@app/notifications"
+  import {notifications} from "@app/notifications"
 
   export let url
   export let room
@@ -13,12 +12,9 @@
 
   const path = makeSpacePath(url, room)
   const channel = deriveChannel(url, room)
-  const notification = notify
-    ? deriveNotification(path, getRoomFilters(room), url)
-    : readable(false)
 </script>
 
-<SecondaryNavItem href={path} notification={$notification}>
+<SecondaryNavItem href={path} notification={notify ? $notifications.has(path) : false}>
   {#if channelIsLocked($channel)}
     <Icon icon="lock" size={4} />
   {:else}