Wire seasonal hymn-doxology into the Matins ferial hymn

The plain ferial hymn's Monastic source (Day1-6 Hymnus,
Psalterium/Special/Matutinum Special.txt) carries a real "*" seasonal-
substitution marker, live-checked against the reference engine. Splits the
hymn's own natural doxology ending into a new per-annum companion file and
swaps it via getHymnDoxologyId/appendDoxology, same pattern already used by
Prime and Compline.

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

src/hours/matins.ts

@@ -76,9 +76,11 @@ import { getPsalmVerses } from '../psalter';
 import { getPsalmsFor, type PsalmRef } from '../psalter/distribution';
 import { getScriptureVerses } from '../scripture';
 import { getOpeningVersicleId } from './opening-versicle';
+import { getHymnDoxologyId } from './hymn-doxology';
 import { applyFlexaMark } from './antiphon';
 import {
   resolveCommon,
+  appendDoxology,
   getDayCollect,
   getOfficeOverrideId,
   resolveOfficeWinner,
@@ -454,7 +456,14 @@ function resolveMatinsHymn(day: LiturgicalDay): ResolvedText {
       return seasonal;
     }
   }
-  return resolveCommon('matins-hymn-ferial');
+  // The plain ferial hymn's own Monastic source (Day1-6 Hymnus, Psalterium/
+  // Special/Matutinum Special.txt) carries a real seasonal-doxology
+  // substitution marker (live-checked 2026-09-03) — unlike the Advent/
+  // Paschaltide seasonal hymns above, whose Monastic forms are each fixed,
+  // non-swapping text, so only this final fallback needs the swap.
+  const body = resolveCommon('matins-hymn-ferial');
+  const doxology = resolveCommon(getHymnDoxologyId(day, 'matins-hymn-doxology-per-annum'));
+  return appendDoxology(body, doxology);
 }
 
 /** The plain ferial weekday nocturn's real antiphoned psalmody — a