feat: accept reaching-defs ddg prov token from codeanalyzer-typescript

[rahlk]

codeanalyzer-typescript emits L3 ddg edges with prov: ["reaching-defs"] — a sanctioned additive deviation from the canonical ssa token (it is reaching-definitions, not SSA form; decision recorded in codellm-devkit/codeanalyzer-typescript#32). The SDK's Pydantic model must accept reaching-defs in the prov literal so it does not reject a valid analysis.json, and should land in lockstep with the analyzer.

Ref: codellm-devkit/codeanalyzer-typescript#32 (part of epic #26).

[rahlk]

Absorbed 2026-07-09 into #240: the cpg Edge.prov is open-vocabulary by design, so the sanctioned reaching-defs token (codellm-devkit/codeanalyzer-typescript#32) parses without a model change. Epic #238.