feat: admin Visas tab — table + edit dialog + visibility toggle

Activates the previously-disabled Visas tab on /admin/logistics.

VisasTab renders a flat table joined per attendee per project, sorted
by status priority. Status filter pills mirror the Confirmations tab.
The header carries a "Visible to teams" Switch backed by a new
logistics.getVisaVisibility query and the existing setVisaVisibility
mutation; toggling it controls whether members see their own status.

VisaEditDialog is a per-row editor with a status dropdown,
nationality input, three native date inputs (invitation / appointment
/ decision), and a notes textarea. No file uploads — the platform
deliberately holds zero document artifacts.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/unit/visa-admin.test.ts

@@ -113,7 +113,11 @@ describe('logistics.listVisaApplications', () => {
 
     expect(result).toHaveLength(3)
     // REQUESTED (0) → APPOINTMENT_BOOKED (2) → GRANTED (3)
-    expect(result.map((r) => r.status)).toEqual(['REQUESTED', 'APPOINTMENT_BOOKED', 'GRANTED'])
+    expect(result.map((r: (typeof result)[number]) => r.status)).toEqual([
+      'REQUESTED',
+      'APPOINTMENT_BOOKED',
+      'GRANTED',
+    ])
     expect(result[0].id).toBe(app.id)
   })
 })