propers: Benedictus antiphons for April's sanctoral entries (8/8)

All 8 authored fresh: Francis of Paola, Leo I, Ss. Tiburtius/Valerian/
Maximus, George, Mark, Vitalis, Robert, Peter Martyr. Several share
one Eastertide Common-of-Several-Martyrs antiphon word for word
(Tiburtius/Valerian/Maximus, George, Vitalis, Peter Martyr) -- each
confirmed independently via its own live query rather than assumed
from the others.

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

TODO.md

@@ -123,7 +123,10 @@ saint has the same kind of mismatch.
   and March 9 always falls within Lent every tested year (2026-2035) — she
   structurally can never win her own day outright under this app's own
   calendar rules, so there's no live-rendered antiphon to source at all.
-- **April-December (87 saints): not started.**
+- **April (8 total): done, all 8.** St. Francis of Paola, St. Leo I,
+  Ss. Tiburtius/Valerian/Maximus, St. George, St. Mark, St. Vitalis,
+  St. Robert, St. Peter Martyr.
+- **May-December (79 saints): not started.**
 - **~52 temporal entries: not started.**
 - **94 `propers: null` saints: not started** — need a collect authored (a
   bigger, separate task) before an antiphon id even has anywhere to attach.