Dynamic right-alignment of dates

[jnd-au]

• Use COLUMNS env var or dynamic terminal width (up to UIWidth max)
• Refresh each time, in case the user’s terminal is resized
• Fix Regression: Dates are truncated #53 (regression since e4e6d44)

This PR also adds some unit test support:

• main.test.go: Stable UTC data model for reproducible tests
• main.test.go: stripAnsiControlSequences to ignore colours (clean test data)
• view_test.go: Use txtar to read, write, and annotate human-readable test data (easy git diffing)
• testdata/view: Test dynamic right-alignment of dates in narrow, medium, and wide cases

[oz]

Thanks for this fix. 😄 🙏🏻

I've rebased the changes on the main branch here, as they were in conflict with commits made after the PR was opened.

Side note: I'm not sure I like refreshing so often, but eh... trade-offs. This is something that could maybe be optimized later. 🔮