fix(of): rename credo to creed, correct three comment inaccuracies

Fix round 1 for Task 3, addressing review findings.

Rename the exported creed function from `credo` to `creed` across the
.ml, .mli and test call sites, so the OF rite bundle can write
`creed = Rubrics_of.creed` with no gratuitous mismatch against
Rite.t's own field name, matching Rite_ef.Rubrics_ef.creed's own
naming. IGMR n. 67's own heading is "Professio fidei" and its body
says "Symbolum", never "Credo" -- documented as a comment on the
now-correctly-named function rather than kept as the exported name.
Local test helpers (credo_on_temporal, check_credo, test_credo_*) and
Alcotest description strings keep the Latin shorthand, since only the
call sites against RO.creed needed to change.

Corrected two comment inaccuracies:
- The Annunciation (25 March) is NOT always inside Lent, unlike St
  Joseph (19 March): 25 March sits after Easter's own earliest
  possible date (22 March), so in an early-Easter year (2008, Easter
  23 March) it falls inside the Easter Octave instead, or is
  transferred under Normae n. 60/5. No functional effect (gloria/creed
  read observed/temporal as actually resolved), but the stated reason
  was wrong.
- The Requiem-silence argument's counts: three All Souls Mass
  formularies (not two), and roughly 147 Gloria+Credo markers combined
  elsewhere in the Missal (not "over 150", which conflated Gloria
  alone with the combined figure) -- recounted directly against a
  fresh pdftotext -layout extraction rather than estimated.

Added: an independent corroborating citation for the Holy Thursday /
Easter Vigil Gloria exception, Vigil n. 31 -- the Easter Vigil's own
praenotanda ("VIGILIA PASCHALIS IN NOCTE SANCTA"), a THIRD
independently-numbered rubric set inside the same Missal PDF,
confirming the Vigil's own Gloria directly rather than resting solely
on the Holy Thursday rubric's forward-looking "usque ad" clause.

dune test: exit 0, 845 tests. make check (COLITUR_EXHAUSTIVE_SWEEP=1,
full 1583-9999 sweep): exit 0, 851 tests, 330.3s, both run unpiped in
the foreground. git diff --stat v1.0.0..HEAD -- lib/rites/rite_ef/
lib/kernel/ data/ef/ still empty.

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