Integrate into Arbiter for review queries

[jzonthemtn]

Summary

Expose Arbiter review data as a PhiSQL-queryable table. This enables analytical questions like "which reviewers override most often" and "what entity types have the highest disagreement rate."

Scope

• Arbiter accepts PhiSQL queries via CLI and API
• Reviews exposed as a queryable table (`arbiter.reviews`)
• Cross-tool joins with Phinder findings work (depends on cross-tool join semantics)
• Documentation updated with PhiSQL examples

Acceptance Criteria

• Arbiter exposes review data as a queryable table
• PhiSQL queries against `arbiter.reviews` execute correctly
• At least 3 cross-tool example queries documented (review + findings, review + benchmarks)
• Tests cover query parsing, execution, and join correctness