refactor(Core/UD): unify Word features into UD.MorphFeatures

[hawkrobe]

Dissolves the parallel feature bundles: Core.Word.Features is deleted and Word.features is one UD.MorphFeatures bundle (which gains the missing UD Reflex); Word moves to Core/UD/Word.lean beside Core/UD/Basic.lean and carries an explicit admission rule (a property lives on Word iff a Fragment-free token-level engine reads it).

• wh/finite become derived (pronType ∈ {Int, Rel}, verbForm); vform → UD's verbForm; countable evicted (no token-level readers); valence stays as a Word field for the DG engine, with a TODO to migrate it to a carrier capability.
• MorphRule gains a dedicated valenceRule channel (reciprocal/passive affixes); Stem gains baseValence.
• Local builds skipped per CI-as-gate; expect CI to be authoritative.