test: add runnable smoke tests for examples

[samlaycock]

Summary

Closes #34.

Adds runnable smoke coverage for the examples directory so example drift is caught by the test suite and by the dedicated Bun script.

Changes

• Added test/examples-smoke.test.ts, which discovers every examples/*.ts file and registers one Bun smoke test per example for independent failure reporting.
• Added bun run examples:smoke for running the example smoke coverage directly.
• Made examples/batch-job.ts deterministic by injecting a UserApi dependency instead of performing real network calls during example execution.
• Documented the preferred future-example rule in conventions/TESTING.md: examples must stay deterministic, fast, and free of real network calls.
• Added a patch changeset for the testing/docs coverage improvement.

Verification

• bun run examples:smoke
• bun fmt
• bun lint:fix
• bun test
• bun typecheck
• bun lint

[greptile-apps]

Greptile Summary

Adds runnable smoke coverage for the examples/ directory: a new test file discovers all .ts examples and executes each as a separate Bun subprocess, batch-job.ts is made deterministic via a stubbed UserApi dependency, and the testing convention is documented.

• test/examples-smoke.test.ts registers one test per example file (using readdirSync at module scope), ensuring every example is exercised and failures are reported independently.
• examples/batch-job.ts replaces the live fetch call with an injected UserApi dependency and a stubUserApi implementation, making the example safe to run in CI without network access.
• package.json gains an examples:smoke script and conventions/TESTING.md documents the determinism requirement for future examples.

Confidence Score: 5/5

Safe to merge — changes are additive test infrastructure with no impact on library behaviour.

The diff adds a smoke test harness, a deterministic stub for one example, a new npm script, and a documentation line. No production code is modified, and the approach (per-file subprocesses, module-scope file discovery) is sound.

test/examples-smoke.test.ts has two minor style points worth a quick look before merging.

Important Files Changed

Filename	Overview
test/examples-smoke.test.ts	New smoke test file that discovers and runs each example as a subprocess; bare expect() outside a test block and .quiet() suppressing stderr are minor concerns
examples/batch-job.ts	Refactored to inject a stubbed UserApi dependency instead of making real network calls; deterministic and self-contained
package.json	Adds examples:smoke script pointing to the new test file
conventions/TESTING.md	Documents the new convention: examples must be deterministic, fast, and free of real network calls
.changeset/runnable-examples-smoke.md	Patch changeset entry for the smoke coverage addition

_{Reviews (2): Last reviewed commit: "test: address example smoke review feedb..." | Re-trigger Greptile}