feat: Add User Usage Tracker

[locnguyen1986]

Build a lightweight tracker to monitor key user interactions (e.g., feature usage, session duration).
Suggestions:

• Use anonymized metrics to comply with privacy regulations (GDPR/CCPA).
• Integrate with existing telemetry tools (e.g., Prometheus metrics or OpenTelemetry).
• Focus on high-impact features first (e.g., chat interactions, API calls).
• Why: Provides actionable data for future prioritization without overwhelming the system.