Add as-is decision gate and clarify course defaults

[Carr1005]

Summary

• add an explicit as-is/customize express lane to the pre-build decision gate
• preserve per-row customization while allowing one explicit answer to resolve all rows to their defaults
• distinguish course provenance labels from agent recommendations, including substitution rows
• update the agent-memory course spec to match the refined generation guidance

Why

The existing gate required every decision to be asked individually and treated recommendations as incompatible with course-default provenance. This made the default build path unnecessarily cumbersome and could mislabel substituted implementation defaults as choices the course actually used.

Impact

Builders can explicitly choose the course-default takeaway in one step or customize each decision. The resulting checklist remains complete and visible, while course provenance stays accurate.

Validation

• git diff --cached --check
• reviewed the staged diff and confirmed only the two requested Markdown files were committed