[Auth 114] Add contributor guidance for handling secrets and mock credentials safely

[inteee]

Outcome

Add contributor guidance for handling secrets and mock credentials safely as an intermediate milestone slice for the authentication MVP.

Scope

• Area: Cross-cutting auth docs, QA, and contributor enablement
• Primary workspaces: docs, api, web, mobile, types
• This issue should produce a reviewable contributor-sized implementation, not a micro-task.

Acceptance Criteria

• Implementation matches the shared auth contracts and reset architecture.
• Changes include the necessary tests or validation notes for the affected surface.
• Documentation is updated when the contributor workflow, setup, or behavior changes.
• The result is scoped so it can be reviewed as one issue-focused pull request.

[ohamamarachi474-del]

@ohamamarachi474-del has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

can i work on this issue ???

ℹ️ Repo Maintainers: To accept this application, review their application or assign @ohamamarachi474-del to this issue.