docs: vendor OpenAPI spec locally to fix deploy validation

The hosted spec at api.supermemory.ai/v3/openapi fails Mintlify's OpenAPI
validation: PATCH /brain/models 200 response is missing the required
'description' field, which aborted the whole docs deploy. Vendor the spec
into the repo with the missing description patched, and point both the api
config and the API Reference tab at the local file so deploys no longer
depend on fetching (or the validity of) the live endpoint.

Root-cause fix still needed API-side: add the description to the
/brain/models PATCH route's 200 response in the OpenAPI generator.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

apps/docs/docs.json

@@ -8,7 +8,8 @@
 				"python",
 				"curl"
 			]
-		}
+		},
+		"openapi": "openapi.json"
 	},
 	"colors": {
 		"dark": "#1E3A8A",
@@ -290,7 +291,8 @@
 				"anchors": [
 					{
 						"anchor": "API Reference",
-						"icon": "unplug"
+						"icon": "unplug",
+						"openapi": "openapi.json"
 					}
 				],
 				"tab": "API Reference"