test(differential): refresh the lectio fixture, close 9 entries, add C14

lectio moved 2386a45 -> 3b32c00 (seven EF calendar defects fixed, plus a
sanctoral-generator root-cause fix); the committed fixture predates all
of them. Regenerated with the same command the provenance note already
named (`go run ./cmd/lectio-ef-dump 2005 2050`), read-only against
lectio -- nothing there was touched. New SHA-256 asserted in both the
provenance note and test_differential.ml's fixture_sha256. The dumper's
two new name_en/name_pl columns are kept verbatim (the fixture is meant
to be the exact command's raw output; the comparator already discards
everything past field 7).

Every C-entry's expected_rows was re-derived independently against the
refreshed fixture (a Python re-implementation of diff_fields/
layer_c_reason, cross-checked against the real OCaml comparator's own
failure output), not transcribed from a green run. Nine entries -- C2,
C3, C4, C5, C7, C10, C11, C12, C13 -- now match zero rows and are
closed: sexp row removed, layer_c_reason predicate and its now-dead
helper bindings removed, citation preserved in
docs/research/rules-register.md's new §3d with the specific lectio
commit that fixed each one. C1 (361 -> 368) absorbs C13's former 7 rows
now that lectio's own slug matches there too. C6 (138, unchanged count)
narrows to a slug-only shape now that lectio's rank agrees. C8 (31,
unchanged) survives untouched -- lectio still computes no Rogation days.

C9's old shape ("Joseph observed ON a Lent Sunday") is also closed, but
a narrower, different divergence survived under the same saint's slug: 3
years (2008, 2035, 2046) where Joseph's own congested RG96 walk collides
with the Annunciation's separately-transferred "sedes propria". The old
predicate's broad "any diff involving this slug" match was silently
absorbing both under one citation -- split into a new id, C14, rather
than folded back into C9, since the two are unrelated rules. lectio's
own commit history (09a1444) documents this residual as a gap it
deliberately left unresolved; colitur gives Joseph a real transferred
day either way, which is why C14's verdict stands regardless of a
genuinely open sub-question (recorded in the register, not resolved
here) about which of the two feasts should claim the contested day
first under RG98's "prius impeditum" wording.

Re-triaged the full remaining 4975 raw differences: only 10 distinct
field-diff signatures now, all resolving to Layer A/B noise or the four
surviving citations, 0 unexplained. The crude "Sunday-rank" and "Holy
Thursday" residues the task flagged both fully resolve once the real
Layer A/B machinery runs (season-spelling and week-numbering artifacts,
not substantive divergences) -- see the task report for the derivation.

Teeth proof: perturbing ferial_rank to reproduce C4's old defect made
140 rows reappear as unexplained (the exact prior C4 count), reverted
after capturing the failure message.

277 tests green (dune test) and 278 with COLITUR_EXHAUSTIVE_SWEEP=1 (the
extra case is the 1583-9999 sweep itself).

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