Fix octave day labels: correct commemoration phrasing, closing-day title, and privileged-season precedence

Three related day-label bugs, all found via Aug 19's mislabeled Assumption
octave commemoration:

- A sanctoral winner that displaces the only active octave now shows the
  octave's real "Nth Day within the Octave of X" phrasing (no rank, since
  it's riding along under the winning feast), not a bare feast name.
- An octave's own closing day now titles itself "Octave of X", matching
  the real DO's "in octava" vs. "infra octavam" distinction, instead of
  "8th Day within the Octave of X".
- A sufficiently-ranked octave can now outrank a privileged temporal
  season (e.g. the Immaculate Conception's octave outright winning several
  of its days against Advent, live-verified against Divino Afflatu 1954),
  via a new shared octaveGoverningPrivilegedDay helper used by both the
  day label and the actual office-content resolver. Deliberately excludes
  Christmastide, whose own stacked octaves are structurally already that
  season's temporal content rather than a foreign add-on.

Updates a Matins test fixture that had unknowingly relied on the
Dec 15 bug (Advent ferial + a lone commemorated saint) and splits it into
a clean ferial case plus a dedicated commemorated-saint case.

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

tests/hours/matins.test.ts

@@ -6,7 +6,12 @@ import { getPsalmsFor } from '../../src/psalter/distribution';
 // and TODO.md for why this is a mechanism build with a small content slice,
 // not full-calendar content. Both live-verified against the reference
 // engine (Monastic Tridentinum 1617) before authoring.
-const FERIAL_DATE = '2026-12-15'; // Tuesday of Advent III — plain ferial, no feast collision.
+const FERIAL_DATE = '2026-12-01'; // Tuesday of Advent I — plain ferial, no feast collision.
+// Not Dec 15 (formerly used here): that's actually the Immaculate
+// Conception's own octave closing day (Duplex majus per Divino Afflatu
+// 1954), which now correctly wins outright over Advent's own
+// privileged-feria-minor ferias — see calendar/octaves.ts's
+// octaveGoverningPrivilegedDay — so it's no longer a clean ferial date.
 const SUNDAY_DATE = '2026-09-06'; // 14th Sunday after Trinity — plain Sunday, no feast collision.
 
 describe('resolveOrdo("matins", ...) ferial (1-nocturn) branch', () => {
@@ -37,21 +42,34 @@ describe('resolveOrdo("matins", ...) ferial (1-nocturn) branch', () => {
     expect(ordo.parts.some((p) => p.kind === 'canticle')).toBe(false);
   });
 
-  it("resolves the user's own bible-plan readings for Advent III Tuesday, not the historical lectionary", () => {
+  it("resolves the user's own bible-plan readings for the day, not the historical lectionary", () => {
     const lessons = ordo.parts.filter((p) => p.kind === 'lesson');
-    // 2 bible-plan readings, plus a 3rd: St. Eusebius of Vercelli's own
-    // commemoration reading, generously surfaced per the "commemorations
-    // get their own reading" design (see hours/matins.ts's own header) —
-    // vu places him Dec 15 (a Monastic 1617 same-day redirect), commemorated
-    // under this Advent III Tuesday ferial.
-    expect(lessons).toHaveLength(3);
+    // Plain 2 bible-plan readings on this particular clean ferial (no
+    // commemorated saint here) — see the next test for the 3-reading case.
+    expect(lessons).toHaveLength(2);
     const citations = lessons.map((l) => (l as { text: { citation?: { en?: string } } }).text.citation?.en);
-    expect(citations).toEqual(['Isa 36; Isa 37', 'Sap 14', undefined]);
+    expect(citations).toEqual(['Isa 6; Isa 7', 'Sap 2']);
     // Real content isn't imported yet (Vulgate/Douay-Rheims bulk import is
     // a deferred follow-on) — honest `missing`, not fabricated text.
     expect((lessons[0] as { text: { status: { en?: string } } }).text.status.en).toBe('missing');
   });
 
+  it("adds a 3rd reading for a commemorated saint, generously surfaced per the 'commemorations get their own reading' design (see hours/matins.ts's own header)", () => {
+    // Not FERIAL_DATE: needs an ordinary Advent ferial with a real
+    // commemorated saint and no active octave. St. Bibiana (Simplex) is
+    // the exact case calendar/commemorations.ts's own header cites as
+    // live-verified: merely commemorated under an Advent feria, never
+    // winning outright (Simplex is below privileged-feria-minor's own
+    // Semiduplex threshold). 2025-12-02, a Tuesday, keeps the same 9-psalm
+    // ferial shape as the other tests in this block.
+    const commemoratedOrdo = resolveOrdo('matins', '2025-12-02');
+    const lessons = commemoratedOrdo.parts.filter((p) => p.kind === 'lesson');
+    expect(lessons).toHaveLength(3);
+    const citations = lessons.map((l) => (l as { text: { citation?: { en?: string } } }).text.citation?.en);
+    expect(citations).toEqual(['Isa 6; Isa 7', 'Sap 2', undefined]);
+    expect((lessons[0] as { text: { status: { en?: string } } }).text.status.en).toBe('missing');
+  });
+
   it("matches the first reading (Isaiah) against the seeded per-book responsory pool", () => {
     const lessons = ordo.parts.filter((p) => p.kind === 'lesson');
     const first = lessons[0] as { responsory?: { text: { la?: string } } };