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')
 }

frontend/src/pages/AdminPage.css

@@ -217,6 +217,14 @@
   cursor: pointer;
 }
 
+.admin-token-resend {
+  background: transparent;
+  border: none;
+  color: var(--ds-accent);
+  font-size: 0.76rem;
+  cursor: pointer;
+}
+
 .admin-issue-token {
   display: flex;
   align-items: center;

frontend/src/pages/AdminPage.tsx

@@ -15,6 +15,7 @@ import {
   listSiteInvites,
   promoteUser,
   reactivateUser,
+  resendSiteInvite,
   resetUserPassword,
   revokeSiteInvite,
   sendTestSmtpEmail,
@@ -312,6 +313,15 @@ export function AdminPage() {
     })
   }
 
+  async function handleResendSiteInvite(invite: SiteInvite) {
+    await withBusy(invite.id, async () => {
+      const updated = await resendSiteInvite(invite.id)
+      // Same row, refreshed expiry (a new token/link went out, see
+      // resend_site_invite) -- update in place rather than a full refetch.
+      setSiteInvites((prev) => prev.map((i) => (i.id === updated.id ? updated : i)))
+    })
+  }
+
   async function handleSaveSmtpSettings(e: FormEvent) {
     e.preventDefault()
     setSmtpSaving(true)
@@ -422,6 +432,14 @@ export function AdminPage() {
                   <span className="admin-token-meta">
                     Expires {new Date(invite.expires_at).toLocaleDateString()}
                   </span>
+                  <button
+                    type="button"
+                    className="admin-token-resend"
+                    disabled={busyId === invite.id}
+                    onClick={() => handleResendSiteInvite(invite)}
+                  >
+                    Resend
+                  </button>
                   <button
                     type="button"
                     className="admin-token-revoke"