feat(ADR-0131.G.5): aggregate answer composition — combined/together cues wired, axis lane 20/20, wrong==0 (#197)
Closes the vocabulary gap: `combined` and `together` added to `_Q_TOTAL_RE`
and `_Q_ENTITY_RE` tail alternations. Both map to `entity=None` semantics;
the solver's existing sum path is unchanged.
Ships:
- Parser one-line regex extension (`generate/math_candidate_parser.py`)
- 20-case curated axis lane (`G5_aggregate/v1/`) — 5 shapes × 4 cues
- Runner + byte-equal report (20/20 pass, wrong=0)
- 25 tests covering cue vocab, 2/3-entity sums, degenerate aggregate,
refusals, byte-equality, B3 regression guard, GSM8K safety rail
- ADR-0131.G.5
No admission movement on GSM8K probe (statement-parse bottleneck unchanged).
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