feat(Core): subsumption order on MorphFeatures; unify is lub#122
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Formalizes the information ordering of unification-based grammar ([shieber-1986] §3.2, the depth-1 reentrancy-free fragment) on
UD.MorphFeaturesin newCore/Subsumption.lean: subsumption as a decidablePartialOrder(⊑is≤), the empty bundle as⊥(Shieber's variable),compatible_iff_bddAbove, andunify_isLUBwith the §3.2.3 laws (unify_comm/unify_self/bot_unify) as theorems.compatibleguarded only 6 of 13 option fields, sounifysilently kept the left value on e.g. conflictingvoiceinstead of failing — totalized; commutativity ofunifyis a consequence. Full graph green (6011 jobs), zero downstream flips (agreement goes through the φ-projection).Word.Agree.symm(the docstring's "symmetric tolerance relation", now proven) and the verifiedshieber-1986bib entry.