Revert ordinary-Sunday Semiduplex to transferring, per direct instruction

Keeps Simplex commemorating in place, but a Semiduplex feast on an
ordinary Sunday goes back to transferring off to the next open day —
this app's own design choice, not a correction against a reference
engine. The transfer mechanism is already generic: this file's `decideOccurrence`
only signals "couldn't hold onto this candidate" for the day itself;
calendar/index.ts's resolveDay is what independently checks each
neighboring day's own native occurrence for an incoming transfer and
claims it — no separate lookback logic needed.

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

src/calendar/commemorations.ts

@@ -159,22 +159,28 @@ export function decideOccurrence(
         // Duplex+ wins outright; the Sunday itself is commemorated in return.
         return { winner: sanctoralWinner(sanctoral), commemorations: [{ kind: 'temporal', id: temporalId }] };
       }
-      if (sanctoral.rank !== 'vigil') {
-        // Semiduplex or Simplex: commemorated, not transferred — live-
-        // verified (both Tridentine 1906 and Divino Afflatu 1954, the two
-        // calendar tracks this app blends): St. Gregory Thaumaturgus
-        // (Semiduplex) lands on the 6th Sunday after Epiphany, 2024-11-17,
-        // and is commemorated right there ("Commemoratio: S. Gregorii
-        // Thaumaturgi..."), not pushed to the next open day. Corrects an
-        // earlier, unverified guess that Semiduplex was "too important to
-        // merely commemorate" — Monastic Tridentinum 1617's own structural
-        // rubric *does* transfer him, but precedence here follows Divino
-        // Afflatu, not Monastic 1617's own (see CLAUDE.md).
+      if (sanctoral.rank === 'simplex') {
+        // Too minor to warrant its own day, but a plain commemoration
+        // doesn't cheapen it the way it would a Semiduplex.
         return { winner: temporalWinner, commemorations: [sanctoralCommemoration(sanctoral)] };
       }
-      // A Vigil still transfers (backward, per transferDirectionOf) — a
-      // distinct rule from Semiduplex/Simplex above, not verified against
-      // this same live case and left as-is.
+      // Semiduplex or Vigil: no room here at all, in either direction —
+      // per direct instruction, an ordinary Sunday's own standing pushes
+      // a Semiduplex feast off to the next open day (typically the
+      // Monday right after) rather than downgrading it to a bare
+      // commemoration. This `transfer` signal is only half of the
+      // mechanism: it's just this day noting "I couldn't hold onto this
+      // candidate." The other half — a later day actually claiming a
+      // transferred-in candidate — lives entirely in calendar/index.ts's
+      // resolveDay: for *every* date it resolves, it independently
+      // recomputes `resolveNativeOccurrence` for both the day before and
+      // the day after, checks whether *that* neighbor's own native
+      // occurrence produced a `transfer` pointed this direction, and only
+      // then folds it in via `applyIncomingTransfer`. So "Monday looks
+      // back at the sanctoral calendar to see if Sunday's own candidate
+      // needs a home" isn't a separate mechanism to build — it's the
+      // existing generic transfer-consumption check, which already runs
+      // for every day regardless of category.
       return {
         winner: temporalWinner,
         commemorations: [],