Add OpenAPI smoke tests to PR verification

[Copilot]

Adds smoke coverage for generated Zig clients so PRs verify that OpenAPI examples under openapi/ can generate code and that the generated code compiles. The suite runs specs one at a time with per-spec output to make failing inputs easy to identify.

• Smoke test script

  • Added test/smoke-tests.ps1.
  • Builds openapi2zig unless -UseInstalled is provided.
  • Discovers OpenAPI example specs under openapi/, excluding openapi/json-schema.
  • Generates each supported JSON spec into an isolated .zig-cache/smoke-tests/... folder.
  • Compiles each generated client with a small Zig test harness.
  • Skips YAML by default until YAML input support is available; -IncludeYaml is available for future coverage.

• CI integration

  • Updated the PR smoke-test job to run the new PowerShell smoke suite.
  • Added an explicit 15-minute timeout for the smoke-test step.

• Documentation

  • Documented the smoke test command and expected runtime in README.md.

pwsh ./test/smoke-tests.ps1

[Copilot]

Pull request overview

Adds a PowerShell-based smoke test suite to CI so PRs validate that all example OpenAPI/Swagger JSON specs under openapi/ can (1) generate Zig client code via openapi2zig and (2) successfully compile via a small Zig test harness.

Changes:

• Added test/smoke-tests.ps1 to generate and compile a client per spec with per-spec output directories and logging.
• Updated CI smoke-test job to run the PowerShell smoke suite with a 15-minute step timeout.
• Documented the smoke test command and intent in README.md.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
test/smoke-tests.ps1	Implements per-spec generation + compilation smoke coverage, with JSON-only default and optional YAML inclusion.
README.md	Documents the new smoke test script, what it checks, and expected runtime characteristics.
.github/workflows/ci.yml	Replaces the previous sample generation step with the new smoke test step (pwsh) and adds a timeout.