Improve table context visibility and accessibility

[omercnet]

Summary

This improves the embedded pgpeek table browser so users can always tell which table or view they are looking at, even when the selected sidebar row is off-screen.

Changes

• Add a main-pane context bar showing the current schema/table and row estimate.
• Make the active sidebar item accessible with aria-current and scroll it into view on selection.
• Restyle Export CSV as a clearer action with better contrast across themes.
• Add tab/panel semantics, a skip link, visible focus states, and mobile layout safeguards.
• Document the embedded app console design rules in DESIGN.md.
• Refresh docs screenshots at smaller dimensions so table details are easier to read.

Validation

• npm run coverage

[cubic-dev-ai]

2 issues found and verified against the latest diff

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[cubic-dev-ai]

1 issue found across 3 files (changes from recent commits).

<sub>Tip: Review your code locally with the cubic CLI to iterate faster.

Re-trigger cubic</sub>