Moves generate_incident_summary() to AI service module and refactors code

[mvilanova]

Code Changes Summary

src/dispatch/ai/service.py

• Added imports for Visibility and Incident.
• Simplified the generate_case_signal_summary function by modifying how the response is processed.
• Introduced a new function generate_incident_summary to create summaries for incidents, with checks for visibility, review documents, and plugin availability.

src/dispatch/incident/flows.py

• Replaced the call to incident_service.generate_incident_summary with ai_service.generate_incident_summary in the incident_closed_status_flow function.

src/dispatch/incident/scheduled.py

• Reorganized imports and added import for ai_service.
• Replaced the call to incident_service.generate_incident_summary with ai_service.generate_incident_summary in the incident_report_weekly function.

src/dispatch/incident/service.py

• Removed the generate_incident_summary function, which has been moved to ai_service.

src/dispatch/incident/views.py

• Reorganized imports and added import for ai_service.
• Replaced the call to generate_incident_summary with ai_service.generate_incident_summary in the generate_summary endpoint.