Add checked store and set data

src/app/state.ts

@@ -1,9 +1,10 @@
 import twColors from "tailwindcss/colors"
-import {get, derived} from "svelte/store"
+import {get, derived, writable} from "svelte/store"
 import {nip19} from "nostr-tools"
 import type {Maybe} from "@welshman/lib"
 import {
   ctx,
+  now,
   setContext,
   remove,
   assoc,
@@ -16,6 +17,7 @@ import {
   nthEq,
   shuffle,
   parseJson,
+  prop,
 } from "@welshman/lib"
 import {
   getIdFilters,
@@ -259,6 +261,14 @@ export const deriveEventsForUrl = (url: string, filters: Filter[]) =>
     ),
   )
 
+// Last checked timestamps, notifications
+
+export const checked = writable<Record<string, number>>({})
+
+export const deriveChecked = (key: string) => derived(checked, prop(key))
+
+export const setChecked = (key: string, ts = now()) => checked.update(assoc(key, ts))
+
 // Settings
 
 export const SETTINGS = 38489