Upgrade GPUI Kit 0.7.0

[JetSquirrel]

Upgrade the UI toolkit to GPUI Kit v0.7.0 and adopt what it makes possible.

Changes

• Upgrade to gpui-kit v0.7.0 — pin the toolkit, shell and component catalog to the v0.7.0 tag; open windows through gpui_kit::open_window instead of hand-wrapping a Root. The hidden export window gets the same Root as the main window, fixing a panic when a .dash app raises a dialog during export.
• Underline the failing span when a query errors — parse DuckDB's LINE n caret position into a UTF-8 byte range and mark it in the SQL editor with a wavy underline and faint fill (theme danger color) via v0.7.0's decoration collections. Marks follow edits, stay out of undo history, and clear on the next run.
• Draw dashboard charts honestly — a pivoted bar spec draws one grouped chart instead of one small chart per series, scatter draws unconnected points, and a pivoted line draws lines without the borrowed area fill. Hand-built on gpui_kit::base::plot, which v0.7.0 publishes without the styled component layer. Chart tooltips show the formatted value (4.4M) instead of the raw f64, and x labels spread by a width-aware count so date labels no longer collide at the edges.
• Table and toolbar polish — result and dashboard tables fit column widths to sampled content (CJK-aware, via unicode-width); the title bar and export row compose as Toolbar/ToolbarGroup, gaining arrow-key focus traversal.
• Give EmptyHeader its named slots in relation_panel — the example passed children where the component only accepts media/title/description slots; the empty state failed to materialize and logged an error every frame.