Adds `teaching/math_claim_signature.py` with `lexical_claim_signature()`:
sha256 hex of a normalised lexical token, collapsing two refusal cases on
the same surface token into one teaching-corpus candidate.
Normalisation pipeline (documented in module, breaking-change surface):
1. Lowercase surface
2. Strip string.punctuation from both ends (!"#$%&'()*+,-./:;<=>?@[\]^_`{|}~)
3. Extract token from refusal_detail via r"no primitive or lexicon match for '([^']+)'"
4. Fallback: use stripped-lowercase surface if regex doesn't match
5. Canonical: "lexical:" + extracted_token
6. sha256 hex of UTF-8 bytes → 64-char lowercase hex
Also adds `teaching/math_contemplation.py` (W2-A adapter included as
union-merge; W2-A worktree was not yet dispatched):
- `audit_to_evidence()`: AuditRow iterable → MathReaderRefusalEvidence tuple
- `audit_problem_to_evidence()`: convenience wrapper for tests and W3-A
- Lexical evidence: claim_signature filled; evidence_hash recomputed to include it
- Non-lexical sub_types: claim_signature stays "" (deferred per ADR-0167 §Q1)
Real-data result on audit_brief_11.json:
- 14 distinct lexical tokens → 14 distinct signatures (no false collisions)
- No duplicate tokens in the 50-case sample; dedup logic verified deterministic
Wave 2, parallel with W2-C/D; depends on W1-A branch.
wrong=0 verified by passing regression suite.
