calendar: real occurrence/precedence resolution (feast ranks, sanctoral content)

Replaces the FeastRank placeholder with a real ordered FeastClass (the old
pre-1955 six-level scale) and a new TemporalCategory (privileged/ordinary
Sunday/feria). calendar/commemorations.ts's decideOccurrence encodes the
actual precedence rules as explicit, commented branches per category
rather than the reference engine's own opaque numeric weights — this app
targets one ruleset, so the readability trade-off is worth it. Category
membership (data/calendar/temporal-categories.yml) is a best-effort
reconstruction of the pre-1955 tradition, not sourced from a primary text;
expect corrections.

calendar/feasts.ts resolves real sanctoral candidates, and resolveDay()
wires it all together — occurring/temporalCategory are no longer stubs.
isDoubleOrHigher (hours/antiphon.ts) is now a real comparison instead of
a hardcoded false.

Seeded 7 real saints/feasts, each verified directly against Divinum
Officium's own rank data (not reconstructed from memory) as a small,
growable start: St. Lawrence, the Assumption, St. Augustine, the Nativity
of the BVM, St. Michael, All Saints, the Immaculate Conception.

src/calendar/feasts.ts

@@ -1,6 +1,51 @@
 // Sanctoral occurrence resolution: given a date, which saint(s) are
 // assigned via data/calendar/sanctoral-calendar.yml's day -> saint-id
-// mapping, and their rank/propers/common from data/calendar/saints/<id>.yml.
-// See calendar/temporal.ts for the separate Easter/fixed-date resolution.
-// Unused until milestone 4.
-export {};
+// mapping, and their rank from data/calendar/saints/<id>.yml. See
+// calendar/temporal.ts for the separate temporal-cycle resolution, and
+// calendar/commemorations.ts for how a candidate returned here actually
+// gets weighed against the day's temporal standing.
+//
+// Doesn't resolve clashes *among* multiple saints sharing a date — real
+// practice has its own precedence/commemoration rules for that too, not
+// modeled here. If a day has more than one candidate, calendar/index.ts
+// just picks the highest-ranked as the day's sole sanctoral contender.
+import type { FeastClass } from './types';
+import sanctoralCalendarData from '../data/calendar/sanctoral-calendar.yml';
+
+interface SaintRecord {
+  id: string;
+  name: string;
+  rank: FeastClass;
+  common: string;
+  propers: string | null;
+}
+
+const sanctoralCalendar = sanctoralCalendarData as { days: Record<string, string[]> };
+
+const saintModules = import.meta.glob<{ default: SaintRecord }>('../data/calendar/saints/*.yml', {
+  eager: true,
+});
+
+const saintsById = new Map<string, SaintRecord>();
+for (const mod of Object.values(saintModules)) {
+  saintsById.set(mod.default.id, mod.default);
+}
+
+export interface SanctoralCandidate {
+  id: string;
+  name: string;
+  rank: FeastClass;
+}
+
+/** Which saint(s) (if any) are assigned to this date. `isoDate`'s year is ignored — the sanctoral cycle repeats every civil year. */
+export function getSanctoralCandidatesFor(isoDate: string): SanctoralCandidate[] {
+  const monthDay = isoDate.slice(5);
+  const ids = sanctoralCalendar.days[monthDay] ?? [];
+  return ids.map((id) => {
+    const saint = saintsById.get(id);
+    if (!saint) {
+      throw new Error(`sanctoral-calendar.yml references unknown saint id '${id}'`);
+    }
+    return { id: saint.id, name: saint.name, rank: saint.rank };
+  });
+}