fix: hide default webkit scrollbar button artifact in repo weights table

[edwin-rivera-dev]

Fixes #280

Summary

Fixes a visual artifact on the Onboard → Repositories tab: when the table is scrollable (e.g. Rows ≥ 25), a thin line appears above the vertical scrollbar in the top-right corner.

Root cause

In src/components/repositories/RepositoryWeightsTable.tsx, the <Box> wrapping the description + controls has a borderBottom: '1px solid rgba(255,255,255,0.1)'. That wrapper spans the full component width. The TableContainer beneath it is overflow: auto, so when the scrollbar appears it narrows the scrollable area by ~8px — but the border above doesn't shrink with it, leaving ~8px of border hanging over the top of the scrollbar track. That's the "dash" in the issue.

The sibling LanguageWeightsTable doesn't have this bug because it separates its controls from its table with mb: 3 spacing instead of a full-width border, and the sticky header cells supply their own per-cell borderBottom that naturally stops where the scrollbar starts.

Fix

Match the pattern used by LanguageWeightsTable:

• Remove borderBottom: '1px solid rgba(255,255,255,0.1)' from the outer header wrapper in RepositoryWeightsTable.tsx.
• Replace it with mb: 3 for breathing room.

The sticky-header borderBottom on each TableCell already provides the visible separator between controls and rows, and it correctly shrinks with the scrollable area.

Type of Change

• Bug fix (visual)

Testing

• npm run build
• npm run lint:fix
• Manual on /onboard?tab=repositories: set Rows to 25 → scrollbar appears → no dash above it.
• Manual on /onboard?tab=languages: unchanged (verifies the fix just aligns the two tabs).

Checklist

• No behavior change
• No new dependencies
• One file touched
• Matches the pattern already used by LanguageWeightsTable

Screenshots

[edwin-rivera-dev]

@anderdc can you please review my PR and let me know your feedback?

[anderdc]

The description says this fixes a Chrome ::-webkit-scrollbar-button artifact, but the diff just swaps a borderBottom for a margin on the header wrapper Box. Can you clarify how removing a border between the header and the table addresses a scrollbar pseudo-element issue? The root cause described doesn't match the change.

[edwin-rivera-dev]

Hi @anderdc
You're right - the PR description is stale, my apologies.
I updated the PR description now so it reflects what the diff actually does.
Please review again and let me know asap.
Thanks.