fix(widgets): Add error boundary to widget footer

[priscilawebdev]

Wrap the Widget component's Footer slot in an ErrorBoundary, matching the
existing pattern used for the Visualization slot.

Previously, errors in footer content (e.g. null data passed to rendering
components) would propagate up and crash the entire page. Now footer errors
are contained within the widget frame, showing a WidgetError message while
the rest of the widget (title, visualization) continues to render normally.

This came up from a crash on the agent monitoring page where a null modelId
in the LLM Calls widget footer took down the whole page. The root cause null
check is in #110505 — this PR adds defense-in-depth so similar issues in any
widget footer won't crash the page.

[gggritso]

Makes sense, thanks! Wondering about that Panel change, though! I was thinking that adding a <Container position="relative" (or whatever the syntax is) wrapper around WidgetError to accomplish the same thing might be better. Seems like composing the wrapper is cleaner than adding props to the element

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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