feat(sidebar): navigate search results with arrow keys and open with Enter

[shouwang0527]

Summary

• Arrow keys (up/down) navigate through filtered table results while the sidebar search field is focused
• Enter opens the currently selected table, matching DataGrip's search-then-navigate workflow

Fixes #1280

Implementation

• Added control(_:textView:doCommandBy:) to SidebarContainerViewController to intercept arrow keys and Enter in the native NSSearchField
• Arrow navigation updates sidebarState.selectedTables to move through the filtered list
• Enter triggers the same open-table logic as double-click (including preview window routing)

[github-actions]

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[shouwang0527]

I have read the CLA Document and I hereby sign the CLA.

[shouwang0527]

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