Handle blank database URLs

[mixxorz]

Fixes #27

[Copilot]

Pull Request Overview

This PR ensures that invoking the CLI without specifying a database URL fails fast, surfaces a clear error, and exits with a non-zero status.

• Adds validation in config.initialize to raise an error if url is blank
• Updates the CLI entrypoint to catch that error, print a message, and sys.exit(1)
• Introduces test_no_url and adjusts the existing preference-order test in tests/test_cli.py

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
tests/test_cli.py	Added test_no_url and updated call count assertion in the settings-preference test
dslr/config.py	Added a blank-URL check that raises ValueError
dslr/cli.py	Catches the blank-URL error, prints it in red, and exits 1

Comments suppressed due to low confidence (2)

dslr/config.py:26

• Define and raise a more specific exception (e.g. MissingDatabaseUrlError) instead of the generic ValueError, so consumers can distinguish missing-URL errors from other configuration issues.

        if not self.url:

tests/test_cli.py:261

• [nitpick] Consider adding a unit test directly against config.initialize(url="", debug=False) to verify it raises the expected exception, improving coverage of the validation logic.

    def test_no_url(self, mock_get_snapshots):