feat: add Grammar→CausalSearch bridge and CausalCertificate

CausalBridge: connects GrammarTriangle (text→meaning) to CausalEngine
(Pearl's do-calculus). Maps DependencyType→EdgeType, converts text
fields to fingerprints, provides ingest_text() one-shot pipeline.
11 tests.

CausalCertificate: statistical evidence bundle for causal claims.
Combines Cohen's d effect size, Granger temporal signal, 95% CI,
p-value, Berry-Esseen approximation bound, and NARS truth values.
certify() gates claims through all conditions simultaneously.
13 tests.

https://claude.ai/code/session_01NocTBszN8LoR9Vrc7Tn4oF

Author: claude