fix(ci): restrict docker build to MCP server tags only

Docker images should only be built for MCP server releases (v* tags),
not for Helm chart (nextcloud-mcp-server-*) or Astrolabe (astrolabe-v*)
releases.

Changed trigger from all tags to v* pattern only.

.github/workflows/docker-build-publish.yml

@@ -2,7 +2,8 @@ name: Build and Publish Docker Image
 
 on:
   push:
-    tags: ["*"]
+    tags:
+      - "v*"
 
 jobs:
   build-and-push: