Add St. Francis Xavier (Dec 3) sanctoral content

Own real Oratio and Nocturn 2-3 content (Duplex majus). This was the
only real gap left in December -- the rest of the month was already
complete from the earlier pre-1955 sanctoral pull. No test collisions:
Dec 3 was genuinely open.

This closes out the full-year sanctoral sweep (January-December).

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

src/data/calendar/sanctoral-calendar.yml

@@ -457,6 +457,11 @@ days:
   # Ember Saturday -- a known Mass-vs-Office simplification, same pattern
   # as September's Vigil of St. Matthew.
   "12-02": [st-bibiana]
+  # St. Francis Xavier (Dec 3, Duplex majus, own real Oratio and Nocturn
+  # 2-3 content) -- added by the later full-year sanctoral pull that
+  # otherwise found this month already complete from the earlier
+  # pre-1955 pass.
+  "12-03": [st-francis-xavier]
   "12-04": [st-barbara]
   "12-05": [st-sabbas]
   "12-06": [st-nicholas]