fix(finalist): program-scope guards on enroll/unenroll (code review)

- enrollFinalists: reject a roundId whose competition belongs to a
  different program than input.programId.
- unenroll: reject a project/round pair from different programs before
  any delete.
- Hoist ADMIN_CONFIRM attendee validation to a pre-pass so a bad entry
  in a multi-team batch fails before any project is partially written.
- Add regression tests for both cross-program guards.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/unit/finalist-enrollment.test.ts

@@ -316,6 +316,31 @@ describe('finalist.enrollFinalists', () => {
       }),
     ).rejects.toThrow(/cap/i)
   })
+
+  it('rejects a roundId that belongs to a different program', async () => {
+    const admin = await createTestUser('SUPER_ADMIN')
+    userIds.push(admin.id)
+
+    const a = await setupEnrollFixture(`enroll-xprogram-a-${uid()}`)
+    const b = await setupEnrollFixture(`enroll-xprogram-b-${uid()}`)
+    programIds.push(a.program.id, b.program.id)
+    userIds.push(a.lead.id, a.member.id, b.lead.id, b.member.id)
+
+    const caller = createCaller(finalistRouter, {
+      id: admin.id,
+      email: admin.email,
+      role: 'SUPER_ADMIN',
+    })
+
+    // Program A's project + Program B's LIVE_FINAL round → must be rejected.
+    await expect(
+      caller.enrollFinalists({
+        programId: a.program.id,
+        roundId: b.liveFinalRound.id,
+        enrollments: [{ projectId: a.project.id, mode: 'EMAIL' }],
+      }),
+    ).rejects.toThrow(/does not belong to this program/i)
+  })
 })
 
 // ─── finalist.listEnrollmentCandidates ────────────────────────────────────