Add AgentPond tracing to development examples

[marcusschiesser]

Summary

• add opt-in AgentPond/OpenInference tracing to the executable OpenAI extraction examples
• load the Files SDK exporter through an ESM-compatible bootstrap while keeping the published CommonJS library path unchanged
• flush the trace provider in each example's existing lifecycle and document local Files SDK setup

Tracing stays inactive unless FILES_SDK_PROVIDER is present.

Verification

• npm run build
• npm run test:unit — 84 tests passed
• npm run test:usage with a real gpt-4.1-mini extraction
• agentpond sync — 7 events synced; LangChain generation trace 90a4772486042b9b283d6382d7bf9c95