Add .dockerignore to exclude target/ and node_modules/ from build context

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: danmolitor

.dockerignore

@@ -0,0 +1,7 @@
+engine/target/
+server/target/
+node_modules/
+packages/*/node_modules/
+packages/*/dist/
+packages/core/pkg/
+.git/