fix: truncate table header names with ellipsis instead of overlapping

[vishwakt]

Fixes #2083

Root Cause

Two stacked problems in TabularHeader.tsx:

1. The header label sits in a CSS grid cell without min-w-0, so the grid item cannot shrink below the label's min-content width. Shrinking a column makes the label overflow the header cell and overlap the neighboring column.
2. The text-ellipsis class was gated on a per-column overflow option that the Data Explorer never sets, and without whitespace-nowrap it had no effect even where it was set.

Fix

Header labels now always truncate (min-w-0 + truncate), and string headers carry a title attribute so hovering reveals the full name, as requested in the issue. Columns with a custom headerComponent are left untouched and get no title.

Testing

• Added a component test asserting the title attribute and truncation class, and that custom header components get no title attribute.
• Reproduced the issue's exact steps against a local TinkerPop Gremlin Server seeded with long property names, resizing the header columns smaller. Screenshots below.
• The hover reveal uses the native browser tooltip via the title attribute, which headless screenshots cannot capture, so the capture log verifies the attribute in the DOM instead.

Before (resized columns, header names overlap):

After (same columns, names truncate with an ellipsis; hover shows the full name):