build(deploy): Add configurable Maven mirror

Add MAVEN_MIRROR_URL for 1Panel backend builds so deployments can
use a faster regional mirror or Maven Central based on network access.

Update the 1Panel deployment guide to document the mirror option and
keep first-time Nacos credentials guidance near environment setup.

backend/docker-compose.1panel.yml

@@ -29,6 +29,9 @@ x-backend-build: &backend-build
   context: .
   dockerfile: Dockerfile.service.1panel
 
+x-backend-build-args: &backend-build-args
+  MAVEN_MIRROR_URL: ${MAVEN_MIRROR_URL:-https://maven.aliyun.com/repository/public}
+
 services:
   mysql:
     image: mysql:8.0
@@ -213,6 +216,7 @@ services:
     build:
       <<: *backend-build
       args:
+        <<: *backend-build-args
         MODULE: video-gateway
         JAR_PREFIX: video-gateway
     container_name: haovp-video-gateway
@@ -237,6 +241,7 @@ services:
     build:
       <<: *backend-build
       args:
+        <<: *backend-build-args
         MODULE: video-auth
         JAR_PREFIX: video-auth
     container_name: haovp-video-auth
@@ -260,6 +265,7 @@ services:
     build:
       <<: *backend-build
       args:
+        <<: *backend-build-args
         MODULE: video-user
         JAR_PREFIX: video-user
     container_name: haovp-video-user
@@ -290,6 +296,7 @@ services:
     build:
       <<: *backend-build
       args:
+        <<: *backend-build-args
         MODULE: video-content
         JAR_PREFIX: video-content
         INSTALL_FFMPEG: "true"
@@ -326,6 +333,7 @@ services:
     build:
       <<: *backend-build
       args:
+        <<: *backend-build-args
         MODULE: video-comment
         JAR_PREFIX: video-comment
     container_name: haovp-video-comment
@@ -349,6 +357,7 @@ services:
     build:
       <<: *backend-build
       args:
+        <<: *backend-build-args
         MODULE: video-recommend
         JAR_PREFIX: video-recommend
     container_name: haovp-video-recommend
@@ -372,6 +381,7 @@ services:
     build:
       <<: *backend-build
       args:
+        <<: *backend-build-args
         MODULE: video-admin
         JAR_PREFIX: video-admin
     container_name: haovp-video-admin