[Docs cleanup] API scenario testing docs

[lirenhe]

Context: API scenario testing (OAV) consumes the generated OpenAPI, so the tooling is still valid
Question: do we still need this tool or just make it archive?

Tasks:

• 🟡 documentation/api-scenario/README.md — "Swagger" → "generated OpenAPI"
• 🟡 documentation/api-scenario/how-to/GenerateABasicApiScenario.md — inputs are generated OpenAPI, not hand-authored Swagger
• 🟡 documentation/api-scenario/how-to/MakeTestProxyRecording.md — "Swagger consistency" → "OpenAPI consistency"
• 🟡 documentation/api-scenario/how-to/QuickStart.md — drop AutoRest/readme.md-tag dependency framing
• 🟡 documentation/api-scenario/how-to/ResolveDependencies.md — emphasize generated OpenAPI sources; clarify readmeTag
• 🟡 documentation/api-scenario/references/ApiScenarioDefinition.md — "Swagger operation/OperationId" → "OpenAPI"
• 🟡 documentation/api-scenario/references/Runner.md — replace AutoRest/readme.md config discovery with generated OpenAPI discovery
• 🟡 documentation/api-scenario/references/ErrorCodeReference.md
• 🟡 documentation/api-scenario/references/Variables.md
• 🟡 documentation/api-scenario/references/v1.2/schema.json