Add exception_class_named as 6th v1 axis in filter_score.js

In filter_score.js, add 'exception_class_named' as the 6th axis using the same highSystem/lowSystem evaluator pattern as the existing 5 axes. Scoring 0-3: 0 = no exception classes mentioned anywhere in hypothesis description; 1 = vague acknowledgment only ('edge cases handled by the system', 'exceptions routed appropriately') without named classes; 2 = two or more distinct named exception types without specified routing destinations; 3 = named exception queue with explicit routing per class (e.g. 'enterprise-tier: CSM escalation; compliance dispute: legal review; API-unavailable: 24h defer'). Add to the evaluator instruction: 'Score based on explicitly named situations where the workflow should NOT fire autonomously. Named exception types with routing paths score 2-3. Vague acknowledgment or no mention scores 0-1. Phrases like the system will learn which cases are exceptions score 0.' Add migration s157_add_exception_class_axis.js following the existing s112 migration pattern to add column exception_class_named_score REAL and exception_class_named_spread REAL to the hypotheses table. Update the composite formula to sum all 6 axes (max 18 instead of 15); update the graduation threshold proportionally (from 9/15 = 60% to 10.8/18 = 60% kept constant).

Applied retroactively to 43 S157-graduated candidates: hyp-2026-04-19-3656a0 (ec4507, cited explicit scope exclusions) scores 2-3; hyp-2026-05-06-847f7e (zero exception classes anywhere) scores 0; at least 38 of 43 score 0-1, producing a minimum 2-point composite spread between ROBUST and STRUCTURALLY FRAGILE S157 buckets solely from this axis.

Retroactively score 43 S157-graduated candidates. If ec4507 (the one candidate with named exception queue per S157) scores below 2, the evaluator misreads explicit scope exclusion as something other than exception naming. If 847f7e scores above 0, evaluator is not detecting absence. If more than 8 of 43 score 2-3 (implying more than 18% already have named exceptions, contradicting S157's 1/43 finding), axis is capturing something other than Q3.

Deferred. Engine logic for this proposal is sound or partial, but the build was not prioritised this cycle.