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/presentation-of-the-bvm-antiphon.yml

@@ -0,0 +1,18 @@
+# Read directly from web/www/horas/Latin/Sancti/11-21.txt's own [Ant 1]
+# cross-reference and its English counterpart -- `@Commune/C10:Ant 2_`
+# (Common of the BVM on Saturday) with a feast-specific substitution
+# applied and computed by hand here: `s/Christo:.*/Christo, allelúja./`
+# (Latin) / `s/Christ;.*/Christ, alleluia./` (English) -- truncates the
+# Common's own antiphon after "...Jesu Christo"/"...Jesus Christ" and
+# appends ", allelúja."/", alleluia." instead of continuing with "ora
+# pro pópulo..."/"pray for the people...". Effectively proper to this
+# feast (the substitution isn't shared by any other saint using C10),
+# so authored as its own file via `propers` rather than as a reusable
+# Common template.
+id: presentation-of-the-bvm-antiphon
+text:
+  la: "Beáta Dei Génetrix, María, * Virgo perpétua, templum Dómini, sacrárium Spíritus Sancti, sola sine exémplo placuísti Dómino nostro Jesu Christo, allelúja."
+  en: "O Blessed Mary, * Mother of God, Virgin for ever, temple of the Lord, sanctuary of the Holy Ghost, thou, without any example before thee, didst make thyself well-pleasing in the sight of our Lord Jesus Christ, alleluia."
+status:
+  la: verified
+  en: verified