docs(specs): describe repository created_by and updated_by as recorded

What this changes

S17 and monolith/S05 say a repository's created_by and updated_by stay null "until the full auth integration". That is out of date: the token-exchange validator already supplies the caller's GitLab user id (Identity.GitLabUserID(), the value the Maven and npm version writes record). This MR rewrites those sentences to the behavior the companion code MR ships: both fields carry the GitLab user id of the principal whose request created or last updated the row.

File	Change
docs/specs/S17-rest-management-api.md	The S08 dependency row, the resource-field table row for created_by / updated_by, and the Update section. A request with no GitLab user leaves the stored value as it is, and a body that edits no column writes nothing, the user id included.
docs/specs/monolith/S05-repository-detail.md	Drops the "until its full auth integration" clause from the createdBy / updatedBy null cases.
api/openapi/v1.yaml	Descriptions of created_by and updated_by only. No operation, schema shape, or field changes, so api/bruno/** has nothing to follow.
docs/testing/e2e/management.md	Adds e2e.management.repository.created-by and e2e.management.repository.updated-by.

Merge order

Merge this MR first. The code MR, !3092 (!3092), implements what this one describes.

Not in this MR

• No docs/user/** change: no page there describes repository attribution.
• Repositories created or updated before the code MR lands keep null. The acting user is only knowable at write time, so there is nothing to backfill.

Related to #1261

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