Ratchet governance coverage threshold from 67% toward 80%

[rolandpg]

Context

Per external code review: the governance coverage target was walked back from 80% to 67% to match actual enforcement. This is governance drift in the wrong direction.

Plan

1. Keep CI enforcing at current 67% (no regression)
2. Track delta: current 67%, target 80%
3. Ratchet upward as coverage improves — bump CI threshold each time tests are added
4. Do not lower the doc target again to match reality

Why

For a project positioning itself for CMMC-adjacent use cases, governance drift in either direction is the failure mode we most need to resist.