feat(admin): "Email sent" column in the tickets table

Organizers had no way to see whether a ticket email went out short of
reading the Postfix journal. Derive a column from the flag the mailer
already sets on each ticket (`extra.email_notification_sent`):
"✓ sent" / "not sent" (paid, no delivery yet) / "unpaid" / "no email".

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EYwoAkZZmXMMmaBp4WGUBo

static/js/index.js

@@ -133,6 +133,19 @@ window.PageEvents = {
           {name: 'event', align: 'left', label: 'Event', field: 'event'},
           {name: 'name', align: 'left', label: 'Name', field: 'name'},
           {name: 'email', align: 'left', label: 'Email', field: 'email'},
+          {
+            name: 'email_sent',
+            align: 'left',
+            label: 'Email sent',
+            field: row =>
+              !row.email
+                ? 'no email'
+                : row.extra?.email_notification_sent
+                  ? '\u2713 sent'
+                  : row.paid
+                    ? 'not sent'
+                    : 'unpaid'
+          },
           {
             name: 'registered',
             align: 'left',