Deploy SearxNG on ai-server-4080 for chat_backend grounded search (#10).

Add roles/searxng (compose + JSON-enabled settings), gate with searxng_stack
on ai-server-4080, open UFW 8088/tcp from the LAN. Port 8088 avoids the
dta_webapp :8080 clash; chat_backend must use SEARXNG_BASE_URL=http://10.0.0.128:8088.

roles/searxng/templates/docker-compose.yml.j2

@@ -0,0 +1,23 @@
+# Managed by Ansible (roles/searxng). Do not edit by hand.
+services:
+  searxng:
+    image: {{ searxng_image }}
+    container_name: searxng
+    restart: unless-stopped
+    ports:
+      - "{{ searxng_host_port }}:{{ searxng_container_port }}"
+    volumes:
+      - ./settings.yml:/etc/searxng/settings.yml:rw
+    environment:
+      - SEARXNG_BASE_URL={{ searxng_base_url }}
+    cap_drop:
+      - ALL
+    cap_add:
+      - CHOWN
+      - SETGID
+      - SETUID
+    logging:
+      driver: json-file
+      options:
+        max-size: "10m"
+        max-file: "3"

roles/searxng/templates/settings.yml.j2

@@ -0,0 +1,20 @@
+# Managed by Ansible (roles/searxng). Do not edit by hand.
+# Minimal overlay on SearxNG defaults — JSON format required by chat_backend (#62).
+
+use_default_settings: true
+
+server:
+  secret_key: "{{ searxng_secret_key }}"
+  limiter: false
+  image_proxy: false
+  port: {{ searxng_container_port }}
+  bind_address: "0.0.0.0"
+  base_url: "{{ searxng_base_url }}"
+
+search:
+  safe_search: 0
+  autocomplete: ""
+  default_lang: "en"
+  formats:
+    - html
+    - json