Every surface heading renders smaller than the panel headings under it

[SociableSteve]

Problem

Every surface's h1 renders smaller than the panel headings beneath it. Tailwind's preflight resets
h1 through h6 to font-size: inherit; font-weight: inherit, and no surface sets a size on its own
h1, so a surface heading is body size and weight while Panel's headings are text-lg. The
hierarchy is inverted on all five surfaces.

Spec 10 states the intent and names the client as the side failing it (see the Scales section, and
criterion 11, which holds the token gap between --text-xl and --text-lg rather than the h1 that
should be using it). So the tokens are correct and asserted; nothing consumes them.

Expected outcome

A surface heading reads as a rank above the panel headings under it, which is what spec 10's type
scale already describes and what criterion 11 keeps a gap for:

• Each surface's h1 renders at --text-xl, and no panel heading on that surface renders larger.
• The relationship is asserted rather than left to the stylesheet, so a future surface cannot render
  a headless-looking h1 and pass.
• Spec 10's Scales section stops naming the client as failing this, because it no longer is.

Context

Found while reviewing #95 (spec 10 rewritten against the shadcn/ui reality). Deferred out of that PR
deliberately: it touches five surfaces and interacts with spec 08's heading hierarchy, which is a
behaviour change rather than a documentation one. The spec names the failure honestly in the meantime.

No urgency.