[dagit] Crag: Some nav tweaks

Summary:
A handful of tweaks to the flat jobs list in left nav.

• Fix duplicate keying for name collisions by using the repo address.
• Fix height for scrollable div.
• Truncate job names with ellipsis.

Test Plan: Run Dagit, verify fixes described above.

Reviewers: bengotow

Reviewed By: bengotow

Differential Revision: https://dagster.phacility.com/D8381