fix(tracing): set OTel service.name resource (default codex)

[tyler-b4innova]

Problem

setupInstrumentation() constructs NodeTracerProvider with only spanProcessors and no resource. The provider falls back to defaultResource() → service.name=unknown_service:node (Node argv0).

This makes multi-service Langfuse projects (shared ingest) unable to filter interactive Codex traces by service.name. The sibling Claude Code Python plugin already picks up OTEL_SERVICE_NAME / OTEL_RESOURCE_ATTRIBUTES via the SDK's always-on OTEL env detector.

Fix

• Build a resource with resourceFromAttributes
• Default service.name to codex (override via OTEL_SERVICE_NAME)
• Merge OTEL_RESOURCE_ATTRIBUTES (comma-separated k=v)
• When unset, map plugin config.environment → deployment.environment.name
• Add direct dependency on @opentelemetry/resources

Test plan

• pnpm test (existing suite)
• pnpm run build
• Manual: enable plugin with OTEL_SERVICE_NAME=codex and confirm resource attrs in Langfuse

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[jannikmaierhoefer]

@claude review