Let the candidate resize the test results panel

[domin67]

The fixed drawer can hide long compiler output during an interview. Allow candidates to trade editor space for results while keeping both areas usable and preserving the selected height.

Summary

• Add a vertical splitter between the editor and test results panel.
• Keep both panels usable by limiting the resizable range.
• Support keyboard resizing with arrow keys, Home, and End.
• Preserve the selected panel height across page reloads and window resizing.

Testing

• Added browser tests for dragging, keyboard controls, bounds, and saved height.
• All 8 related browser tests pass.
• Prettier checks pass for all changed files.
• Manually tested dragging, keyboard resizing, bounds, and saved height on Windows 11 with Google Chrome.

Closes #94

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Summary by cubic

Lets candidates resize the test results panel during an interview, so long compiler output no longer gets hidden by the fixed drawer. Adds a draggable splitter with keyboard support that preserves the selected height, while bounds keep both the editor and results area usable.

• The splitter supports arrow keys, Home, End, and Enter to reset, and stores the height in localStorage.
• Minimum size keeps the expanded "Add a case" form and results toggles visible; maximum size leaves a short, usable editor.
• The editor's old 25rem minimum height was removed so the drawer can reach its bounds without overflowing.
• The divider is hidden when execution is disabled.
• The drawer reclamps to fit when the window or surrounding editor content shrinks, without discarding the saved height, which is restored when space returns.

^{Written for commit ea26024. Summary will update on new commits.}

[jserv]

With a saved height the drawer keeps its fixed flex-basis when #results-toggle collapses #results-body, so collapsing the results leaves an empty block under the toggle instead of giving the room back to the editor as it did before. Let a collapsed drawer size to its content, e.g. .test-drawer:has(#results-body[hidden]) { flex-basis: auto; }, and report the measured height in aria-valuenow while collapsed.

[jserv]

When execution is disabled, renderRuntimeConfig hides .test-drawer but not #test-drawer-resizer, and .test-drawer-resizer { display: block } shows it at every width. The candidate gets a 1rem divider in the tab order that resizes nothing, and an arrow key there saves a height measured against the hidden drawer (bounds collapse to 0), which a later session with execution on then restores. Hide the handle next to the drawer with nodes.testDrawerResizer.hidden = !editorOptions.execution.

[jserv]

room depends on the editor toolbar's height, which changes without any window resize: the sidebar divider narrowing the panel until the toolbar wraps, or applyLanguages(spec) filling the tabs in after init(). attachSplitter reclamps only on window resize, so a saved height can exceed the new max and leave the editor under 6rem until the window changes size. As a follow-up in web/splitter.js, reclamp from a ResizeObserver on the editor stack, the way compactJimStageBesideNarrowPanel already watches its panel.

[ColtenOuO]

Please squash the commit.

[ColtenOuO]

LGTM.

[jserv]

Thank @domin67 for contributing!