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/calendar/saints/presentation-of-the-bvm.yml

@@ -0,0 +1,24 @@
+# Read directly from the reference engine (`../divinum-officium-reference`,
+# per memory vu-reference-engine-file-layout, not a live query): untagged/
+# default [Rank] block of `web/www/horas/Latin/Sancti/11-21.txt` -- "In
+# Præsentatione Beatæ Mariæ Virginis;;Duplex majus;;4;;ex C11". Previously
+# excluded entirely under a stale "fixed BVM feast, excluded per the
+# usual convention" note in sanctoral-calendar.yml's own November comment
+# -- wrong, same class of error as our-lady-of-the-snows.yml. Unlike her,
+# this feast DOES have a real, unique [Oratio] of its own (see
+# presentation-of-the-bvm-collect.yml) and Nocturn 2 vita content
+# (Lectio4-6, St. John Damascene + St. Ambrose on the Blessed Virgin).
+# Her [Ant 1] is a substituted Common text (`@Commune/C10:Ant 2_`, with a
+# truncate-and-add-alleluia edit specific to this feast -- see
+# presentation-of-the-bvm-antiphon.yml), effectively proper by the same
+# "own [Name]/edit makes shared-formula text proper" reasoning as
+# st-lucy-collect.yml, so authored via `propers` rather than a Common
+# fallback. No Lectio7-9 override in her own file (defers to Commune/
+# C11's own Nocturn 3, same as our-lady-of-the-snows.yml's — see that
+# file's own Nocturn 3 comment for why it's duplicated rather than
+# cross-referenced).
+id: presentation-of-the-bvm
+name: "The Presentation of the Blessed Virgin Mary"
+rank: duplex-majus
+common: common-of-the-bvm
+propers: "presentation-of-the-bvm"