Add KB governance review controls

[WalksWithASwagger]

Summary

• Add knowledge_base/governance.yaml support for canonical voice anchors and ignored KB files.
• Add reviewer actions to KB audit warnings and a pre-generation governance warning.
• Add KB dialog controls plus docs/tests for private, stale, duplicate, and oversized context policy.

Verification

• PYTHON=/Users/kk/Code/spektorAI/venv/bin/python make lint
• PYTHON=/Users/kk/Code/spektorAI/venv/bin/python make test -> 285 passed
• PYTHON=/Users/kk/Code/spektorAI/venv/bin/python make eval-fixture
• git diff --check

Closes #49

[github-actions]

Agentic PR Review

Verdict: needs-human

Checks:

• Linked issue via Closes #...: yes
• Issue acceptance criteria found: 4
• PR verification section present: yes
• PR acceptance self-check present: no
• PR self-check covers issue acceptance: no
• Diff within v1 limits: yes
• Missing acceptance coverage:
  • Profile KB audit separates stale, duplicate, private-looking, and oversized findings into clear reviewer actions.
  • A reviewer can mark canonical voice anchors and intentionally ignored files without editing code.
  • Generation surfaces a concise warning when selected profile context has unresolved governance findings.
  • Docs explain the private/stale policy and how future agents should treat flagged context.

This PR is not blocked from human review, but the agentic gate is not satisfied.