Milestone audit now reads existing VERIFICATION.md files from phases
(already created during execute-phase) rather than spawning verifiers
again. Aggregates tech debt and deferred gaps, then runs integration
checker for cross-phase wiring. Adds tech_debt status for non-blocking
accumulated debt.
Also adds VERIFICATION.md to phase completion commit in execute-phase.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>