Simplify `get_database_url` default handling with `or`

[nanotaboada]

Problem

databases/player_database.py::get_database_url:

database_url = os.getenv("DATABASE_URL")
if not database_url:
    storage_path = os.getenv("STORAGE_PATH", "./players-sqlite3.db")
    database_url = f"sqlite+aiosqlite:///{storage_path}"
return database_url

The "declare, then reassign inside an if" shape is a common C#-ism. Python
expresses "use this, otherwise the fallback" with or.

Proposed Solution

def get_database_url() -> str:
    """Return the async database URL from environment variables."""
    storage_path = os.getenv("STORAGE_PATH", "./players-sqlite3.db")
    return os.getenv("DATABASE_URL") or f"sqlite+aiosqlite:///{storage_path}"

Semantic nuance worth understanding (and maybe a comment): or treats an
empty-string DATABASE_URL as unset — same as the current if not database_url. If "set but empty" should be distinct from "unset", the test is
os.getenv("DATABASE_URL") is None instead.

Suggested Approach

1. Collapse the body to the or expression above.
2. Keep the module-level DATABASE_URL / _connect_args logic downstream
   unchanged.
3. Run uv run pytest.

Acceptance Criteria

• get_database_url returns a single or expression
• Empty / unset DATABASE_URL still falls back to SQLite
• STORAGE_PATH override still honoured
• All tests pass
• CHANGELOG.md updated

References

• Python docs — Boolean operations (or)
• os.getenv