Add separate SSE backend for secure Server-Sent Events support

Creates two backends per domain:
1. Regular backend - Uses http-server-close for better security and
   connection management (prevents connection exhaustion attacks)
2. SSE backend - Optimized for Server-Sent Events with:
   - no option http-server-close (allows long-lived connections)
   - option http-no-delay (immediate data transmission)
   - 6-hour timeouts (supports long streaming sessions)

Frontend routing logic:
- Detects SSE via Accept: text/event-stream header or ?action=stream param
- Routes SSE traffic to SSE-optimized backend
- Routes regular HTTP traffic to standard secure backend

This approach provides full SSE support while maintaining security for
regular HTTP traffic (preventing DDoS/connection flooding attacks).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

templates/hap_subdomain_acl.tpl

@@ -1,4 +1,13 @@
-    
+
     #Subdomain method {{ domain }}
-    acl {{ domain }}-acl hdr(host) -i {{ domain }}
-    use_backend {{ name }}-backend if {{ domain }}-acl
+    acl {{ name }}-acl hdr(host) -i {{ domain }}
+
+    # Detect Server-Sent Events (SSE) connections for {{ domain }}
+    # SSE uses Accept: text/event-stream or ?action=stream query parameter
+    acl {{ name }}-is-sse hdr(accept) -i -m sub text/event-stream
+    acl {{ name }}-is-sse-url urlp(action) -i -m str stream
+
+    # Route SSE traffic to SSE-optimized backend, regular traffic to standard backend
+    use_backend {{ name }}-sse-backend if {{ name }}-acl {{ name }}-is-sse
+    use_backend {{ name }}-sse-backend if {{ name }}-acl {{ name }}-is-sse-url
+    use_backend {{ name }}-backend if {{ name }}-acl