fix: ignore nested node_modules in Docker

Add **/node_modules pattern to prevent Docker overlay conflicts
when hoisted mode creates nested symlink structures.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

.dockerignore

@@ -1,5 +1,6 @@
 # Ignore development files
 node_modules
+**/node_modules
 .next
 .git
 .github