Add the ability to resend unaccepted invites (#60)

Previously the only way to resend was to re-invite the same email from
scratch, creating a whole new invite row. Adds a "Resend" action next
to Revoke on each pending invite -- rotates the token and refreshes the
7-day expiry on the same row (the old link stops working the moment
it's used, same instinct as a password-reset resend), then re-sends
the invite email.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/api/admin.ts

@@ -83,6 +83,13 @@ export function revokeSiteInvite(inviteId: string): Promise<SiteInvite> {
   return apiFetch<SiteInvite>(`/api/admin/invites/${inviteId}`, { method: 'DELETE' })
 }
 
+// #60: same invite row, not a new one -- a fresh token/expiry, and the old
+// link stops working the moment this is called (see the backend's own
+// resend_site_invite for why).
+export function resendSiteInvite(inviteId: string): Promise<SiteInvite> {
+  return apiFetch<SiteInvite>(`/api/admin/invites/${inviteId}/resend`, { method: 'POST' })
+}
+
 export function getSmtpSettings(): Promise<SmtpSettings | null> {
   return apiFetch<SmtpSettings | null>('/api/admin/settings/smtp')
 }