Simplify notification badges, improve performance (#57)

Co-authored-by: Jon Staab <shtaab@gmail.com>

src/app/components/EventActivity.svelte

@@ -1,17 +1,18 @@
 <script lang="ts">
   import {onMount} from "svelte"
-  import {max, formatTimestampRelative} from "@welshman/lib"
+  import {max, gt, formatTimestampRelative} from "@welshman/lib"
   import {COMMENT} from "@welshman/util"
   import {load} from "@welshman/net"
   import {deriveArray, deriveEventsById} from "@welshman/store"
   import type {TrustedEvent} from "@welshman/util"
   import {repository} from "@welshman/app"
-  import {notifications} from "@app/util/notifications"
+  import {deriveChecked} from "@app/util/notifications"
   import Reply from "@assets/icons/reply-2.svg?dataurl"
   import Icon from "@lib/components/Icon.svelte"
 
   const {url, path, event}: {url: string; path: string; event: TrustedEvent} = $props()
 
+  const checked = deriveChecked(path)
   const filters = [{kinds: [COMMENT], "#E": [event.id]}]
   const replies = deriveArray(deriveEventsById({repository, filters}))
   const lastActive = $derived(max([...$replies, event].map(e => e.created_at)))
@@ -26,7 +27,7 @@
   <span>{$replies.length} {$replies.length === 1 ? "reply" : "replies"}</span>
 </div>
 <div class="btn btn-neutral btn-xs relative hidden rounded-full sm:flex">
-  {#if $notifications.has(path)}
+  {#if gt(lastActive, $checked)}
     <div class="h-2 w-2 rounded-full bg-primary"></div>
   {/if}
   Active {formatTimestampRelative(lastActive)}