fix: tighten body validation and stream timeout handling

[francoischalifour]

Summary

• Validate --input and @file JSON bodies before they reach API execution.
• Split live stream timeout handling so connect and read phases are enforced independently.
• Expand CI and integration coverage for OpenAPI generation, upsert, and timeout behavior.

Testing

• Added unit coverage for invalid and valid @file JSON payloads.
• Added live stream timeout tests for connect-only and read-timeout paths.
• Extended the shell integration flow to cover upsert by primary key.