refactor(Core/Probability/Choice): dissolve SemiorderRanking bridge

[hawkrobe]

Deletes the early-days SemiorderRanking bridge file — a §1.G↔§2.F synthesis that Luce 1959 explicitly disclaims (p. 34, fn. 5) — generalizing its real content into the files that own it, and fixing the attribution errors the primary source revealed.

• RationalAction: pChoice_eq_div/pChoice_pos/pChoice_lt_of_score_lt become public API; new pChoice_pair ties pChoice to pairwiseProb, retiring the fromScale embedding and the Unit-state specialization.
• RankOrderings: general-state rankProb_pos, rankProb_swap_div, rankProb_swap_lt_of_score_lt; the product decomposition is relabeled as Luce's ranking postulate (previously mis-cited as "Theorem 9") with the §2.F page range corrected; missing plackett-1975/marden-1995 bib entries added.
• ChoiceApproximations: corrects the module docstring's semiorder axiom list, derives jndL_trans from the interval condition + I-reflexivity, drops the unused DecidableEq requirement; two Studies files lose spurious RationalAction imports.