fix(python): resolve full-corpus shape findings

[zmaril]

Summary

• resolve the parenthesized with-item ambiguity found by the locked Python corpus
• make positionless CPython AST hulls token-aware, including comment keywords, with-item parentheses, and bare-CR trivia
• restore queryable field correspondences, classify the TryStar final-body Known Deviation, and add exact regression fixtures
• bind the fresh shape and sweep evidence to the corpus lock and grammar revision

Evidence

• focused shape fixtures: 6 files, 267 oracle nodes, zero findings
• full shape: 296,567 checked, 1,787 skipped, 215,213,266 oracle nodes; zero boundary, kind, mapping, or field findings
• full sweep: 297,252 / 298,354 pass; 7 grammar-gap, 12 version-policy, 1,083 noise
• status --check: Python evidence current
• cargo test --workspace
• tree-sitter corpus: 16 / 16
• negative corpus: 32 / 32 rejected
• generated parser: byte-stable with tree-sitter CLI 0.26.12

Closes #154