Add 4 more fixed Lord's/BVM feasts, and fix Our Lady of the Snows' Nocturn 3

Finding of the Holy Cross (May 3), the Transfiguration (Aug 6), the
Exaltation of the Holy Cross (Sep 14), and Dedication of the Basilica of
the Most Holy Savior (Nov 9, the Lateran) were all excluded under the
same stale "fixed feast of the Lord, not modeled" note that turned out
wrong for Our Lady of the Snows. All four have real, complete content in
the reference engine. Presentation of the BVM (Nov 21) was excluded
under the equivalent "fixed BVM feast" note and is added the same way.

- finding-of-the-holy-cross: fully proprium, own collect/antiphon/Matins
  throughout; now correctly outranks
  ss-alexander-eventius-theodulus-and-juvenal, matching what that
  saint's own file already documented as the live reality.
- transfiguration: same proprium shape. Its subordinate saints (Ss.
  Xystus/Felicissimus/Agapitus) stay excluded -- blocked by the real,
  separate octave/subordination-rendering gap, not by an unmodeled
  Transfiguration.
- exaltation-of-the-holy-cross: reuses the Finding of the Holy Cross's
  content wholesale (ex Sancti/05-03) -- collect/antiphon via a cross-id
  `propers` pointer, Matins nocturn-readings duplicated (no cross-id
  lookup exists for that mechanism).
- dedication-of-the-basilica-of-the-most-holy-savior: reuses the
  existing Common-of-a-Dedication (collect-c8, benedictus-antiphon-
  common-of-a-dedication), real unique Nocturn 2 vita of her own. Her
  secondary, St. Theodore, stays excluded for the same
  octave/subordination reason as above.
- presentation-of-the-bvm: real unique collect of her own; her
  Benedictus antiphon is a substituted Common reference
  (truncate-and-add-alleluia edit specific to this feast), authored as
  her own file.

Also: our-lady-of-the-snows.yml was missing its own Nocturn 3 (she
defers to Commune/C11's own Gospel-incipit-plus-Bede-homily, same as
Presentation of the BVM) -- added.

Test updates (not regressions): three tests had fixed proof dates
colliding with the newly-added feasts, updated to reflect the new,
correct behavior. npm test (365 tests) and tsc --noEmit both pass.

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

src/data/propers/common/finding-of-the-holy-cross-antiphon.yml

@@ -0,0 +1,12 @@
+# Read directly from web/www/horas/Latin/Sancti/05-03.txt's own [Ant 1]
+# and its English counterpart -- fully proper text, not a Common
+# template. Also used by exaltation-of-the-holy-cross.yml, which points
+# its own `propers` here directly rather than duplicating this file
+# (her `ex Sancti/05-03` Rule reuses this content wholesale).
+id: finding-of-the-holy-cross-antiphon
+text:
+  la: "O Crux, * splendídior cunctis astris, mundo célebris, homínibus multum amábilis, sánctior univérsis: quæ sola fuísti digna portáre taléntum mundi, dulce lignum, dulces clavos, dúlcia ferens póndera; salva præséntem catérvam in tuis hódie láudibus congregátam. (Allelúja, allelúja.)"
+  en: "O Cross, * surpassing all the stars in splendour, exceeding dear to all Christian people and world-renowned, holiest of earth's treasures: which only wast counted worthy to hold aloft the Price of our Redemption: sweet is thy wood and sweet thine iron, but sweetest of all the Burden that hung on thee! O that all who come this day to celebrate thy praises may find in thee salvation. (Alleluia, Alleluia.)"
+status:
+  la: verified
+  en: verified