feat: add configurable knowledge rules and exit policy

[EmersonBraun]

Summary

• add versioned configurable rule evaluation over ReconciliationReportV1
• provide default, recommended, and strict modes with CLI > config > preset > default precedence
• support rule severity overrides, ignores, critical entities/paths, conservative centrality risk, and deterministic exit codes
• add ak-docs rules run <report.json> with JSON/text output and exit codes 0/1/2
• preserve existing documentation quality and gate behavior

Issue

Closes #104

Dependency

This PR is stacked on #116 (feat/#103-reconciliation).

Verification

• pnpm typecheck
• npm test — 237 tests passed, including all plugin contract suites
• npm run coverage — 91.13% statements, 77.71% branches, 95.00% functions, 93.38% lines
• npm run build

[EmersonBraun]

Code review

No blocking issues found in the #104 implementation.

The rule engine centralizes policy without duplicating reconciliation, keeps default mode non-blocking, validates configuration before evaluation, supports deterministic severity/ignore/critical-path behavior and CLI exit codes, and leaves existing gate behavior intact. Static centrality is explicitly framed as a review signal rather than runtime availability.

Local verification: 237 tests passed, 91.13% statements coverage, typecheck/build passed.