feat(API): improve post /projects/{project_id}/figma_attachments/{figma_attachment_id}/keys documentation

[Stephen Lumenta (sbl)]

Improves the documentation for post /projects/{project_id}/figma_attachments/{figma_attachment_id}/keys: 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.

Closes DEVEX-118

🤖 Generated with Claude Code

[github-actions]

API changelog (oasdiff)

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

5 changes: 1 error, 1 warning, 3 info
error	[request-body-added-required] at doc/compiled.json
	in API POST /projects/{project_id}/figma_attachments/{figma_attachment_id}/keys
		added required request body

warning	[request-parameter-removed] at doc/compiled.json
	in API POST /projects/{project_id}/figma_attachments/{figma_attachment_id}/keys
		deleted the `path` request parameter `id`
		This is a warning because some clients may return an error when receiving an unexpected parameter. It is recommended to deprecate the parameter first.

info	[response-non-success-status-added] at doc/compiled.json
	in API POST /projects/{project_id}/figma_attachments/{figma_attachment_id}/keys
		added the non-success response with the status `401`

info	[response-non-success-status-added] at doc/compiled.json
	in API POST /projects/{project_id}/figma_attachments/{figma_attachment_id}/keys
		added the non-success response with the status `403`

info	[response-non-success-status-added] at doc/compiled.json
	in API POST /projects/{project_id}/figma_attachments/{figma_attachment_id}/keys
		added the non-success response with the status `422`