Add database connection utility

[Copilot]

Adds a minimal Python database connection utility to address the "connect to database" request.

Changes

• db_connect.py — get_connection(db_url=None) / close_connection(conn) API
  • Defaults to SQLite via DB_PATH env var (no extra deps)
  • Accepts a SQLAlchemy URL for PostgreSQL, MySQL, etc.
  • Proper engine disposal on close; descriptive errors for bad URLs / failed connections
• requirements.txt — commented-out optional drivers (SQLAlchemy, psycopg2, mysqlclient)
• README.md — usage docs for both SQLite and SQLAlchemy-backed databases
• .gitignore — excludes *.db files and Python cache

Usage

from db_connect import get_connection, close_connection

# SQLite (default)
conn = get_connection()

# PostgreSQL (requires: pip install sqlalchemy psycopg2-binary)
conn = get_connection("******localhost:5432/mydb")

close_connection(conn)

DB_PATH env var overrides the default SQLite path (database.db).