Add automatic SSE detection and support to backend template

Changes:
- Detect SSE via Accept header (text/event-stream) or ?action=stream parameter
- Disable http-server-close to allow long-lived SSE connections
- Enable http-no-delay for immediate event delivery
- Set 1-hour timeouts for SSE support (also fine for normal requests)
- Force Connection: keep-alive for detected SSE requests

Benefits:
- SSE now works automatically without special backend configuration
- Fixes transcription server display disconnection issues
- Normal HTTP requests still work perfectly
- No need for separate SSE-specific backends

Fixes: Server-Sent Events timing out through HAProxy

templates/hap_backend.tpl

@@ -1,5 +1,25 @@
 
 backend {{ name }}-backend
+    # Detect Server-Sent Events (SSE) connections
+    # SSE uses Accept: text/event-stream or ?action=stream query parameter
+    acl is_sse hdr(accept) -i -m sub text/event-stream
+    acl is_sse_url urlp(action) -i -m str stream
+
+    # Disable http-server-close from defaults to allow SSE long-lived connections
+    # Normal HTTP requests still work fine without this option
+    no option http-server-close
+
+    # Enable http-no-delay for immediate data transmission (good for SSE and general performance)
+    option http-no-delay
+
+    # Extended timeouts to support SSE long-lived connections
+    # These values also work fine for normal HTTP requests
+    timeout server 1h
+    timeout http-keep-alive 1h
+
+    # Ensure keep-alive connection for SSE requests
+    http-response set-header Connection keep-alive if is_sse or is_sse_url
+
     option forwardfor
     # Pass the real client IP to backend (from proxy headers or direct connection)
     # This is crucial for container-level logging and security tools
@@ -7,9 +27,8 @@ backend {{ name }}-backend
     http-request set-header X-Real-IP %[var(txn.real_ip)]
     http-request set-header X-Forwarded-For %[var(txn.real_ip)]
     {% if ssl_enabled %}http-request set-header X-Forwarded-Proto https if { ssl_fc }{% endif %}
-    
-    
+
+
     {% for server in servers %}
     server {{ server.server_name }} {{ server.server_address }}:{{ server.server_port }} {{ server.server_options }}
     {% endfor %}
-