Wire seasonal hymn-doxology into every plain-default Vespers hymn

Sunday's hymn ("Lucis Creator") is the one case whose Monastic source text
carries a real "*" seasonal-substitution marker (live-checked); every other
key (Mon-Sat, Advent, Lent, Passiontide, Paschaltide) is wired the same way
anyway as a deliberate broadening beyond the source, at the user's request
("the doxology is a neat way to stay tuned in to the season... we're doing a
remix, not a copy"). Each hymn's own natural ending is split into a matching
per-annum companion file, so a season/feast with no override reproduces the
original text exactly; only Nat/Epi/Pasch/Asc/Pent/Corp/Heart and the two
feast/date overrides from the previous commit actually change anything.

Real visible effect: hymns shown during Christmastide/Epiphanytide/Corpus
Christi/Sacred Heart (none of which get a distinct seasonal hymn, so these
were always the plain weekday defaults) now pick up the right doxology
instead of a generic ending; Ascensiontide and the Pentecost octave now
diverge from the rest of Paschaltide's doxology mid-season.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AGjUyhUZJaSjiniEmnLdak

src/data/propers/common/vespers-hymn-lent-doxology-per-annum.yml

@@ -0,0 +1,7 @@
+id: vespers-hymn-lent-doxology-per-annum
+text:
+  la: "Præsta, beáta Trínitas,\nConcéde, simplex Únitas;\nUt fructuósa sint tuis\nJejuniórum múnera.\nAmen."
+  en: "We pray thee, Holy Trinity,\nOne God, unchanging Unity,\nThat we from this our abstinence\nMay reap the fruits of penitence.\nAmen."
+status:
+  la: draft
+  en: draft