feat(era): enable tracing by default and add OpenTelemetry GenAI instrumentation

[enriquekalven]

Overview

This pull request enables OpenTelemetry tracing by default for the Economic Research Agent (ERA) during deployment to Vertex AI Reasoning Engine, establishing telemetry parity with other production agents (such as the On-Brand Media Agent).

Key Changes

• Enabled Tracing in AdkApp: Set enable_tracing=True in the deployment configuration (deploy.py) to automatically capture Reasoning Engine runtime telemetry and execution traces.
• Added GenAI SDK Instrumentation: Added opentelemetry-instrumentation-google-genai to requirements.txt and pyproject.toml to automatically hook into Google GenAI SDK calls, exporting LLM latency, token usage metrics, and step-level traces to Google Cloud Trace and Vertex AI Agent Observability.

Validation

• Verified that uv sync correctly resolves the new OpenTelemetry instrumentation package.
• Confirmed clean application of deployment configuration changes against main.