Feat: add Review insights to harness get pr + standalone list commands

[BlueLabelscotch]

Summary

Surfaces additional Harness review-insight data in the CLI:

• harness get pr now converts to handler_type: workflow and best-effort appends
  two sections below the existing PR table — Insight (risk summary) and
  Review Groups (risk-bucketed changed files). If either call fails, get pr
  still succeeds and simply omits that section; no change to existing get pr
  behavior otherwise. Sections are skipped for machine formats (json/yaml/etc.).
• Three more data points are exposed as standalone list commands:
  • list pr_suggested_reviewer <repo_id>/<pr_number>
  • list pr_suggested_label <repo_id>/<pr_number>
  • list pr_success_criterion <repo_id>/<pr_number>

Changes

• pkg/spec/code.spec.yaml: get pr → handler_type: workflow; new nouns/commands
  for pr_insight, pr_review_group, pr_suggested_reviewer, pr_suggested_label,
  pr_success_criterion.
• modules/code/insight.go (new): GetPRWorkflow — fetches the base PR (hard fail,
  unchanged behavior), then best-effort fetches Insight and Review Groups, logging
  and skipping on failure. Includes reviewGroupTextFormatter for readable output.
• modules/code/code.go: registers the new workflow and text formatter.
• modules/code/insight_test.go (new): httptest-backed coverage.