docs(leads): document Leads store migration and payment UI fix; note tests update

src/lib/stores/ae_events_stores__leads.svelte.ts

@@ -0,0 +1,21 @@
+/**
+ * ae_events_stores__leads.svelte.ts
+ *
+ * Svelte 5 PersistedState store for the Exhibitor Leads module local config.
+ * Replaces the `events_loc.leads` sub-object from the Svelte 4 persisted store.
+ *
+ * localStorage key: 'ae_leads_loc'
+ * Version gate:     AE_LEADS_LOC_VERSION in store_versions.ts
+ *
+ * Session state (non-persisted) stays in `events_sess.leads` — same pattern as
+ * pres_mgmt and badges.
+ *
+ * Usage:
+ *   import { leads_loc } from '$lib/stores/ae_events_stores__leads.svelte';
+ *   leads_loc.current.auth_exhibit_kv   // read
+ *   leads_loc.current.tab[exhibit_id] = 'list'  // write
+ */
+import { PersistedState } from 'runed';
+import { leads_loc_defaults } from './ae_events_stores__leads_defaults';
+
+export const leads_loc = new PersistedState('ae_leads_loc', leads_loc_defaults);