Feat/table fullscreen

[uditkumar01]

Description

Add fullscreen view for tables, matching the existing mermaid chart fullscreen pattern. Tables with many columns are difficult to read in constrained widths. This adds an expand button with sticky headers, copy/download controls, and keyboard dismiss.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Performance improvement
• Refactoring (no functional changes)

Related Issues

Resolves #389, #386

Changes Made

• Add TableFullscreenButton component with opaque overlay, sticky headers, and Escape to dismiss
• Support granular controls.table config for copy, download, and fullscreen
• Extract shared scroll lock utility to lib/scroll-lock.ts, replacing duplicates in link modal and mermaid fullscreen
• Add [data-streamdown="table-fullscreen"] styling selector
• Document table fullscreen in styling docs

Testing

• All existing tests pass
• Added new tests for the changes
• Manually tested the changes

Test Coverage

• Granular table control toggling (show-controls.test.tsx)
• Fullscreen open/close, Escape key, scroll lock, button states (table-fullscreen.test.tsx)

Checklist

• My code follows the project's code style
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• My changes generate no new warnings or errors
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have created a changeset (.changeset\free-years-swim.md)

Changeset

• I have created a changeset for these changes

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