feat(openapi): add optional description field to workspace API key schemas (#13993)

* feat(openapi): add optional description field to workspace API key schemas

Add an optional `description` property (type: string) to three
workspace API key schemas in openapi.yaml:

- Inline request body of createWorkspaceApiKey (POST /api/workspace/api-keys)
- WorkspaceApiKey (list/info schema)
- WorkspaceApiKeyCreated (creation response schema)

The field is not added to any `required` array, making it fully
backward-compatible with existing clients.

Refs: BE-1005, BE-1004

Co-authored-by: Matt Miller <mattmillerai@users.noreply.github.com>

* fix(openapi): mark description nullable in workspace API key response schemas

Per CodeRabbit review on PR #13993: the underlying DB column is nullable
varchar (default ''), so the response schemas should permit null to match
stored data reality. Without nullable: true the OpenAPI contract would
require coercion on the handler side or risk a contract violation.

Request schema unchanged — clients shouldn't be sending null on create.

openapi.yaml

@@ -4160,6 +4160,9 @@ paths:
                 name:
                   type: string
                   description: Display name for the API key
+                description:
+                  type: string
+                  description: User-provided description for the key
       responses:
         "201":
           description: API key created
@@ -7682,6 +7685,10 @@ components:
           type: string
         name:
           type: string
+        description:
+          type: string
+          nullable: true
+          description: User-provided description
         prefix:
           type: string
           description: First few characters of the key for identification
@@ -7708,6 +7715,10 @@ components:
           type: string
         name:
           type: string
+        description:
+          type: string
+          nullable: true
+          description: User-provided description
         key:
           type: string
           description: Full API key value (only returned on creation)