Bug: Make SideEditorLink accessible (non-interactive span with click handler) ​

[Shristibot]

The SideEditorLink component uses a non-interactive span with an onClick handler to focus the editor, but it is not keyboard- or screen‑reader accessible.

Files/areas
app/components/SideEditorLink/SideEditorLink.tsx (around lines 14–24)
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Problem
SideEditorLink renders a span element with an onClick handler to move focus to the editor.
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This element does not have role="button", a tabIndex, or keyboard event handlers (Enter/Space), so it cannot be activated via keyboard or announced correctly by assistive technologies.
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Proposed solution
Change the span to a semantic element for the clickable control.
Update styles as needed so the button matches the existing visual design, instead of using a styled span.
If a non-button element must be retained, add role="button", tabIndex={0}, and an onKeyDown handler that triggers the same behaviour on Enter and Space.
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I’m happy to open a PR implementing this change if this approach looks acceptable.