fix(infra): remove buffer/compress from llm-api for real SSE streaming

- llm-api uses llm-chain instead of common-chain
- llm-chain excludes buffer & compress middlewares
- Prevents Traefik from buffering streaming SSE responses
- Each token is now flushed immediately

infra/traefik/dynamic/apps.yaml

@@ -27,7 +27,7 @@ http:
         - websecure
       tls: {}
       middlewares:
-        - common-chain@file
+        - llm-chain@file
       service: llm-api-service
 
     # ── Tools (Document Scanner & Media Processing) ──

infra/traefik/dynamic/middlewares.yaml

@@ -61,6 +61,14 @@ http:
             - "^/wp-login\\.php"
             - "^/config\\.php"
 
+    # ── LLM Stream Chain (no buffer/compress — SSE needs real-time) ──
+    llm-chain:
+      chain:
+        middlewares:
+          - secure-headers
+          - retry
+          - rate-limit
+
     # ── Common Chain ──
     common-chain:
       chain: