fix(create-architecture): unprime step-07 validation checklist (#2292) (#2347)

step-07-validation template shipped with all 16 completeness checkboxes
pre-checked and Overall Status hard-coded to READY FOR IMPLEMENTATION,
defeating the gate. Reset checkboxes to unchecked, replace status with a
templated choice tied to the checklist and gap analysis, and instruct the
agent to only mark items the validation actually confirms.

Closes #2292