docs: describe the artifact fields in the get snapshot response, starting with deployment_diff #403

Problem

The Get snapshot API reference declares artifacts as Artifacts · object[] with artifacts[]: type object and no field-level descriptions. None of the fields inside an artifact are documented anywhere. deployment_diff is the clearest case: it appears only as raw example output on the kosli get snapshot client reference page, with no explanation of what it means or when it is present.

Expected Behavior

/api-reference/snapshots/get-snapshot describes the fields of an artifact object, including a deployment_diff object with each sub-field explained:

• diff_url
• previous_git_commit
• previous_git_commit_url
• previous_fingerprint
• previous_artifact_name
• previous_artifact_compliance_state
• previous_running
• previous_trail_name
• previous_template_reference_name

It should also state what "previous" is measured against, when deployment_diff is absent, for example the first time an artifact appears in an environment, and which sub-fields can be null.

Current Behavior

Readers have to reverse-engineer the semantics from a sample payload on the client reference page.

Use Case

Anyone consuming the snapshot API programmatically, for lead-time or change reporting, needs to know whether deployment_diff is a reliable pointer to the artifact it replaced.

Suggested Approach

The descriptions belong in the API schema so the generated reference picks them up, rather than being hand-written on the docs page. This issue covers the docs side once the schema carries them.