ci: switch back to node:20-alpine for faster SSH installation

Optimize CI performance by using Alpine Linux with faster package management.

Problem:
- node:20-slim took 11+ minutes to install SSH client due to slow network
- Debian-based package management is slower than Alpine's apk

Solution:
- Switch back to node:20-alpine
- Use apk add --no-cache openssh-client rsync
- Alpine's package management is much faster

Benefits:
- Faster SSH client installation (seconds vs minutes)
- Smaller image size
- Better performance in CI environment

This should significantly reduce build time.

.woodpecker.yml

@@ -1,5 +1,5 @@
 variables:
-  - &node_image node:20-slim
+  - &node_image node:20-alpine
 
 steps:
   install-deps:
@@ -125,7 +125,7 @@ steps:
     commands:
       - echo "Checking SSH client availability"
       - which ssh && echo "SSH client found" || echo "Installing SSH client"
-      - apt-get update && apt-get install -y openssh-client rsync
+      - apk add --no-cache openssh-client rsync
       - echo "Building production artifacts"
       - npm run build
       - echo "Build completed"