Add OpenTelemetry decision tracing

[lleonardo-franco]

Summary

• add the optional TealOTelPlugin backed by OpenTelemetry with injected-tracer support
• emit decision, module, guardrail, and cost spans with decision attributes, span links, and baggage attributes
• expose the v1.2 integration publicly and document a Jaeger/OTLP setup with mock-tracer coverage

Validation

• npx tsc --noEmit
• npm run build:types
• npm test -- --runInBand --no-watchman (95 suites, 2372 tests)

Resolves agentguard-ai/tealtiger#120