test(oracle): compare the observed day's identity, not only rank/colour

Layer 4 (test_oracle.ml, vs missalemeum) compared the observed
celebration's rank and colour and stopped there -- it never checked
whether the observed day is actually the RIGHT one. Holy Family (11
January 2026: oracle title "The Holy Family: Jesus, Mary & Joseph")
is rank 2/white on both sides purely by coincidence -- an ordinary,
unnamed Sunday and Holy Family share both -- so this layer has been
silently blind to the missing feast since it was built.

Adds Observed_identity_mismatch/Observed_identity_unresolved,
following the shape and honesty of yesterday's commemoration-identity
comparison (Comm_identity_mismatch/Comm_identity_unresolved): colitur
identifies its own observed day by slug, missalemeum by an English
title, and the bridge is Celebration.t.names, read directly off
LD.observed. That name is only ever set for a SANCTORAL-origin
celebration -- a TEMPORAL-origin one (an ordinary Sunday, a feria, a
movable named feast) carries none, so most of the 730 days in the
fixture window land in Observed_identity_unresolved, not a clean
match. That is counted and reported, never silently skipped -- the
same discipline this file already applies to an unresolvable
commemoration.

WIP, expected red: 399 days now show observed-identity-unresolved
with nothing in the allow-list naming it, and five of the six
existing M-series entries whose own diff shape is checked by exact
list equality (M1, M2, M3, M13, M16) lose their match now that this
axis widens their diff set. Landed on its own, ahead of any
production fix, so it is the regression net the following commits are
checked against rather than a change bundled in alongside the fix
they enable. The next commits widen those five entries' own diff
shapes and add the new bucket's own cited allow-list entry, then build
Holy Family itself.

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