Add 6 more April saints previously never added

St. Isidore of Seville, St. Vincent Ferrer, St. Hermenegild, St. Anselm,
St. Fidelis of Sigmaringen, St. Peter Canisius -- April complete.
St. Peter Canisius is the second common-of-a-confessor-doctor saint
(after St. John Damascene in March), same benedictusCommon reuse
pattern. St. Hugh, Abbot (Apr 1) checked and correctly skipped: his own
file is Commemoratio-rank with only a collect, no Lectio content at
all to source.

npm test (365 tests) and tsc --noEmit both pass.

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

src/data/propers/common/st-vincent-ferrer-collect.yml

@@ -0,0 +1,24 @@
+# Read directly from web/www/horas/Latin/Sancti/04-05.txt's own
+# [Oratio] and its English counterpart.
+id: st-vincent-ferrer-collect
+text:
+  la: |
+    Orémus.
+    Deus, qui Ecclésiam tuam beáti Vincéntii Confessóris tui méritis et prædicatióne
+    illustráre dignátus es: concéde nobis fámulis tuis; ut et ipsíus instruámur exémplis
+    et ab ómnibus ejus patrocínio liberémur advérsis.
+    Per Dóminum nostrum Jesum Christum, Fílium tuum: qui tecum vivit et regnat in unitáte
+    Spíritus Sancti, Deus, per ómnia sǽcula sæculórum.
+    ℟. Amen.
+  en: |
+    Let us pray.
+    O God, Who wast pleased to enlighten thy Church through the worthy deeds and Gospel
+    preaching of thy blessed Confessor Vincent, grant unto us thy servants grace so to
+    order our lives after his example, that we, being helped by his protection, may by
+    thee be ever delivered from all evil.
+    Through Jesus Christ, thy Son our Lord, Who liveth and reigneth with thee, in the
+    unity of the Holy Ghost, God, world without end.
+    ℟. Amen.
+status:
+  la: verified
+  en: verified