feat: add AI clinical alert worker and frontend alert listener

[phertyameen]

Closes #122

This pr Implements a background AI alert system triggered by the VitalsCreated event.

• Added EventEmitter listener and async worker to process vitals without blocking API responses
• Sends encounter context to Gemini with strict JSON response enforcement
• Persists alerts to ClinicalAlertModel when red flags are detected
• Added frontend polling/WebSocket listener for encounter alerts
• Displays non-intrusive, dismissible toast/sidebar alert in the encounter UI

Includes a manual test trigger for the worker while the Vitals API is still in progress.

[inteee]

Great work on this. I’ve reviewed the changes and everything looks good. Approved.