fix: resolve SQLITE_CANTOPEN with Docker volume permissions

[VishnuByrraju]

Problem

When running Atom in Docker with a host-mounted volume for /app/data, the SQLite database fails with SQLITE_CANTOPEN because the non-root nextjs user (uid 1001) cannot write to the root-owned mounted directory.

Root Cause

The Dockerfile switches to a non-root user before starting the app, but host-mounted volumes are typically owned by root. The nextjs user lacks write permissions to create or modify the SQLite database files.

Solution

• Added docker-entrypoint.sh that runs as root on startup, fixes ownership of /app/data to nextjs:nodejs, then drops privileges via su-exec before starting the Node.js server
• Installed su-exec in the Docker image for secure privilege dropping
• Added .gitattributes to ensure shell scripts maintain LF line endings across platforms

Changes

• Dockerfile: Added su-exec package, entrypoint script copy, replaced USER/CMD with ENTRYPOINT
• docker-entrypoint.sh: New entrypoint handling volume permissions
• .gitattributes: Enforce LF endings for .sh files