feat: Add ms-marco-MiniLM-L-12-v2 model, tokenizer, and configuration files.

chore: Update MongoDB connection URL and password in environment and config files.

refactor: Streamline backend data directory setup, update frontend Next.js type paths, and improve gitignore files.

chore: Add .gitignore to prevent node_modules from being committed.

feat: Add `venv/` to `.gitignore` to exclude virtual environment directories.

first commit