calendar: occurrence engine v2 — real rank thresholds, transfers, collisions

Corrects and completes the occurrence rules, based on a design discussion
plus one concrete data point: St. Anthony Abbot (plain Duplex) was found
outright winning against an ordinary Sunday in the real Monastic 1617
engine, which the old duplex-1-classis-only threshold got wrong.

- FeastClass gains `vigil`, inserted between `simplex` and `semiduplex` —
  one ordering that correctly serves both "does this win against a Sunday"
  (vigil behaves like simplex there) and "which of two saints wins a
  landing-day collision" (vigil beats simplex, loses to semiduplex).
- LiturgicalDay.occurring (a flat OccurringFeast[] that could only ever
  express a losing *sanctoral* candidate) is replaced by `winner:
  DayWinner` + `commemorations: Commemoration[]` — a discriminated list
  that can hold the temporal day itself, one or more sanctoral entries, or
  (not built yet, but the shape already accommodates it) a future octave
  kind.
- commemorations.ts: ordinary Sundays let Duplex+ win outright (Sunday
  commemorated in return), Semiduplex/Vigil transfer elsewhere (too
  substantial a feast to cheapen with a bare commemoration), Simplex stays
  and is commemorated. Privileged Sundays never displace; Duplex-majus+
  commemorated, everything else transfers.
- collision.ts (new): resolves two sanctoral candidates wanting the same
  day (a transfer landing on an already-occupied day, or two native
  saints sharing a date) — duplex > semiduplex > vigil > simplex, loser
  always commemorated, ties favor the native occupant.
- temporal-id.ts (new): maps any date to one of the 52 real Sunday-collect
  ids from the previous commit, so a temporal winner/commemoration can
  actually be looked up, not just labeled "temporal" in the abstract.
- index.ts's resolveDay orchestrates all of it, including the actual
  Monday/Saturday transfer mechanism. Landing on a privileged feria (the
  concrete case: Holy Week, right after Palm Sunday) is explicitly
  deferred rather than guessed at — it needs its own Easter-keyed lookup
  table, the same way the reference engine handles it.

Added the Vigil of St. Lawrence (Aug 9) as real content specifically to
exercise the backward-transfer rule end-to-end: Aug 9, 2026 is a Sunday,
so the vigil transfers cleanly back to Saturday, verified by a new
integration test alongside the unit-level rule and collision tests.

src/hours/antiphon.ts

@@ -1,4 +1,4 @@
-import type { OccurringFeast } from '../calendar/types';
+import type { DayWinner } from '../calendar/types';
 import { isAtLeast } from '../calendar/commemorations';
 
 export interface SplitAntiphon {
@@ -31,13 +31,12 @@ export function splitAntiphon(text: string): SplitAntiphon {
  * said before the psalms (the full text is always said after, regardless
  * of rank).
  *
- * Only asks whether the day's *winning* feast (not a merely-commemorated
- * one) is Double-or-higher — a privileged Sunday with nothing occurring,
- * or a commemorated low-rank saint, both correctly return false here. A
- * Sunday being "privileged" doesn't by itself make this true; that's a
+ * Only asks whether the day's *winner* (not a merely-commemorated feast)
+ * is Double-or-higher — a privileged Sunday with nothing winning, or a
+ * commemorated low-rank saint, both correctly return false here. A Sunday
+ * being "privileged" doesn't by itself make this true; that's a
  * `TemporalCategory` question, not a `FeastClass` one.
  */
-export function isDoubleOrHigher(occurring: OccurringFeast[]): boolean {
-  const winner = occurring.find((feast) => !feast.commemorated);
-  return winner ? isAtLeast(winner.rank, 'duplex') : false;
+export function isDoubleOrHigher(winner: DayWinner): boolean {
+  return winner.kind === 'sanctoral' && isAtLeast(winner.rank, 'duplex');
 }