feat(API): improve patch /projects/{project_id}/screenshots/{id} documentation

[Stephen Lumenta (sbl)]

Improves the documentation for patch /projects/{project_id}/screenshots/{id}: sharper descriptions, parameter docs, error responses, and usage examples.

Drafted with AI assistance and grounded in the API implementation. Please review for technical accuracy before merging; nothing is merged automatically.

🤖 Generated with Claude Code

[github-actions]

API changelog (oasdiff)

Doc-only edits (descriptions, examples) do not appear here.

2 changes: 1 error, 0 warning, 1 info
error	[request-body-media-type-removed] at doc/compiled.json
	in API PATCH /projects/{project_id}/screenshots/{id}
		removed the media type `application/json` from the request body

info	[request-body-media-type-added] at doc/compiled.json
	in API PATCH /projects/{project_id}/screenshots/{id}
		added the media type `multipart/form-data` to the request body