Summary

Implements a default per-client fallback for HOST_DATA_DIR and updates .gitignore.

Problem

• Unset HOST_DATA_DIR led to anonymous volumes in Docker Compose.
• The default './data' directory (or any local data directory) was not ignored by git, risking accidental tracking of large chain datasets.

Solution

• Updated docker-compose.yml to use a client-specific fallback: ${HOST_DATA_DIR:-./${CLIENT:-reth}-data}.
• Added /data/ to .gitignore to cover the most common fallback path.

Verification

• Verified volume mapping correctly defaults to ./reth-data (or equivalent).
• Verified that local data directories are correctly ignored.

Impact

Prevents accidental repository bloat and ensures predictable data persistence.