Redesign the node wizard

[tomasz-zajac-oss]

The node wizard from #109 worked but looked dated: a narrow box, step chips wrapping onto two lines, small form fields. This restyles it. Behaviour is unchanged.

What changed

• Layout: two columns.
  • Sidebar: the element type (icon tile + name) and a vertical stepper. Visited steps get a check; you can click any step.
  • Main column: a progress bar, "Step n of N", the step title as a large heading, and its guidance underneath.
• Fields:
  • larger inputs with a focus ring;
  • enums with up to 6 options render as chips, longer ones stay a select;
  • booleans render as a switch;
  • in a step with only one field, the label is hidden visually (it repeated the heading) but kept for screen readers.
• Relations: candidates are selectable cards with the type's icon and colour, a filter field when there are more than 6, and a "n selected" counter.
• EARS step: the composed sentence shows in a preview card.
• Polish:
  • blurred backdrop, entry and step transitions (none under prefers-reduced-motion);
  • a close button;
  • keyboard hints (⌘↵ / Esc) in the sidebar;
  • a single column below 720 px.
• Contrast: in the dark theme the primary button and the active step use a deeper blue than --accent, so white text reaches 4.5:1 (it was 2.5:1).

Tests

• Only one e2e assertion changed: Status is now a radio chip, not a select.
• npm test and npm run typecheck pass.
• E2E: 53/54. The one failure, in folders.spec.ts (markdown-folder persistence), doesn't touch the wizard. It passed 18/18 when that spec was re-run on its own, so it looks flaky under the full parallel run.
• Checked by screenshot in the web build: ADR (title, context, relations) in the dark theme, Requirement (sentence, EARS fields) in the light theme, and phone width.

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