feat: bring Huf Data Table builder form to Add-Tool-form UX maturity

[esafwan]

Summary

Brings the Huf Data Table create/edit schema-builder form (Table Settings panel, Field
Properties panel, field type selector, field list canvas) up to the same visual maturity as
the "Add Tool" form (ToolCreationForm.tsx/ToolFormModal.tsx), which the user called out
as the reference standard for box/border/color quality.

Two passes:

1. Design-token corrections (text-muted-foreground -> text-steel, stray radius classes).
2. Structural pass: explicit bordered/boxed sections (matching the reference's
   rounded-none border ... p-4 grouping pattern), varied surface colors for depth
   (bg-panel/bg-paper-deep), and bordered header separators — the first pass alone was
   color-token-only and didn't actually close the "maturity" gap, which was structural, not
   color. Caught this by directly comparing screenshots before committing to it, not by
   trusting the diff size.

No behavior change — field add/remove/reorder, type selection, table settings, and delete
confirmation all work exactly as before.

Screenshots (live bench, before → after)

Table Settings panel:
Before:
After:

Field Properties panel:
Before:
After:

Test plan

• yarn typecheck — 0 errors
• yarn lint — 0 errors (60 pre-existing unrelated warnings)
• Verified live on bench before and after each pass; confirmed no functional regression

[esafwan]

Superseded by consolidated Data Tables PR #460, now included in integration PR #468.