feat: Migrate from Socket.IO to Server-Sent Events (SSE)

- Replace Socket.IO with SSE for real-time server-to-client communication
- Add SSE service with client management and topic-based subscriptions
- Implement SSE authentication middleware and streaming endpoints
- Update all backend routes to emit SSE events instead of Socket.IO
- Create SSE context provider for frontend with EventSource API
- Update all frontend components to use SSE instead of Socket.IO
- Add comprehensive SSE tests for both backend and frontend
- Remove Socket.IO dependencies and legacy files
- Update documentation to reflect SSE architecture

Benefits:
- Simpler architecture using native browser EventSource API
- Lower bundle size (removed socket.io-client dependency)
- Better compatibility with reverse proxies and load balancers
- Reduced resource usage for Raspberry Pi deployment
- Standard HTTP-based real-time communication

🤖 Generated with [AI Assistant]

Co-Authored-By: AI Assistant <noreply@ai-assistant.com>

deploy/k8s/registry-secret.yaml

@@ -0,0 +1,8 @@
+apiVersion: v1
+data:
+  .dockerconfigjson: eyJhdXRocyI6eyJnaXRlYS1odHRwLnRhaWxkYjM0OTQudHMubmV0Ijp7InVzZXJuYW1lIjoid2lsbCIsInBhc3N3b3JkIjoiWU9VUl9BQ1RVQUxfR0lURUFfUEFTU1dPUkQiLCJlbWFpbCI6IndpbGxAdGFpbGRiMzQ5NC50cy5uZXQiLCJhdXRoIjoiZDJsc2JEcFpUMVZTWDBGRFZGVkJURjlIU1ZSRlFWOVFRVk5UVjA5U1JBPT0ifX19
+kind: Secret
+metadata:
+  name: regcred
+  namespace: adopt-a-street-prod
+type: kubernetes.io/dockerconfigjson