Define Downstream Rollout and Maintenance Guidance

[FMCalisto]

This issue tracks the guidance needed for teams that create repositories from this source template.

Scope:

• define the minimum post-template setup steps for downstream repositories
• confirm which files and settings should always be customized after template creation
• clarify how the source template should evolve without breaking downstream maintainers

Relationships:

• informed by discussion Which Optional Extensions Should Stay Outside the Default Template? #7, Which Optional Extensions Should Stay Outside the Default Template?
• informed by discussion What Should Remain Mandatory in Downstream Repositories? #8, What Should Remain Mandatory in Downstream Repositories?

Acceptance criteria:

• downstream maintainers have a clear setup and review path after creating a repository from the template
• required customization points are documented in one coherent flow
• the source template and downstream expectations are aligned

Validation expectations:

• review the checklist and README against the intended downstream workflow
• verify that the documented setup path is complete and internally consistent