Fix dashboard dates and stabilize model loading

[deBrian07]

Summary

This PR fixes:

• Display dashboard game dates in Eastern Time, matching the games calendar.
• Add --port to start_app.py so the web app can run on a non-default port when 5000
  is occupied.
• Fail at startup when DATABASE_PATH is missing or the configured database does not
  exist.
• Replace the serialized Tree model with stable XGBoost JSON model files and load only the
  selected predictor, avoiding the PyTorch/XGBoost runtime conflict.
• Make the API test select a game from the configured database rather than relying on a
  stale hardcoded game ID.
• Ignore local database downloads, accidental placeholder databases, and local Neovim
  downloads.

Testing

python -m pytest -q