Fix Christmas Octave Sunday's occurrence precedence (was backwards)

christmastide's Sunday was coded privileged-sunday (Advent's own tier),
which live-checking against the reference engine shows is wrong: on
every one of the three real collision dates (St. Stephen/John/Holy
Innocents, all Duplex-II-classis, falling on the Sunday within the
Octave) the saint wins outright and the Sunday is merely commemorated --
the reverse of what privileged-sunday would produce (Sunday stays
primary, saint just gets a nod). St. Silvester (plain Duplex, Dec 31)
confirms the same live. Reclassified to ordinary-sunday, which matches
all four checked cases: Duplex+ wins outright (Stephen/John/Innocents/
Silvester), Semiduplex still transfers off the Sunday rather than
winning (St. Thomas Becket, unaffected by the fix either way), and a day
with no saint at all resolves to the Sunday cleanly.

Found while pulling christmas-octave-sunday's own Benedictus antiphon
from the reference engine's dedicated Tempora/Nat1-0 proper and noticing
this app's own occurrence resolution didn't match what the live engine
showed for the Sunday's real collision dates.

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

TODO.md

@@ -213,11 +213,28 @@ Urban I/Eleutherius/John I do have content -- they just needed a very
 late test year). Every pre-existing antiphon file that predated this
 pass has now been checked against a live Monastic query; most needed
 correction (confirmed Roman-rite sourced), a handful already matched.
-- **All ~52 temporal entries: done** (see the section above for method and
-  the one deliberate exception, `christmas-octave-sunday`).
+- **All ~52 temporal entries: done, including `christmas-octave-sunday`**
+  (see the section above for method and its own correction).
 - **94 `propers: null` saints: not started** — need a collect authored (a
   bigger, separate task) before an antiphon id even has anywhere to attach.
 
+### Bug found and fixed while pulling christmas-octave-sunday's antiphon
+
+`data/calendar/temporal-categories.yml` had christmastide's own Sunday
+coded `privileged-sunday` (Advent's tier — never displaced short of
+Duplex-majus+, and even then only commemorated in return). Live-checking
+all three Duplex-II-classis "Comites Christi" collision dates (St.
+Stephen/John/Holy Innocents falling on the Sunday, plus St. Silvester,
+plain Duplex) showed the exact reverse: the saint wins outright every
+time, the Sunday only commemorated — `ordinary-sunday`'s rule, not
+`privileged-sunday`'s. Fixed by reclassifying christmastide's `sunday` to
+`ordinary-sunday` (the `feria` side, `privileged-feria-minor`, was
+already correct and untouched). New tests in
+`tests/calendar/december-sanctoral.test.ts` cover both directions: the
+saint winning on the three verified collision dates, and St. Thomas
+Becket (Semiduplex) still transferring off the Sunday rather than
+winning, unchanged by the fix.
+
 ### Bug found while checking February's results, not yet fixed
 
 `hours/resolve-common.ts`'s `splitNamedAntiphon` always marks its output