[FEATURE] Let a published Design System theme the new-chat usage stats card (opt-in, token-based)

What

Allow the color / typography / density tokens from a user's already-published Design System to style the "usage stats" card shown on the Code home / new-chat page (Overview / Models, sessions, tokens, heatmap). Gated behind a single opt-in toggle.

Why this is safe (and not the thing that was deliberately closed)

This is not user HTML or JS injected into the app. The app keeps rendering the card with its own code — it only reads declarative tokens (colors, font, spacing/density) from the Design System the user already published through Claude. That is the exact trust model Design Systems already use for decks, designs and artifacts: no untrusted code executes. So it does not re-open the surface that remote-debugging / HTML injection is fused shut to protect.

Why users want it

The new-chat page is the first thing you see every session. Letting it match your own published Design System makes the space feel like yours. It is a natural extension of a feature you already shipped — the Design System simply applies in one more place.

Keep it small / low risk

• Start with re-color + font + density of the existing card layout, not arbitrary replacement.
• Opt-in, default unchanged — zero risk to anyone who does not turn it on.
• No new rendering engine, no user code path: the renderer stays yours, only the tokens are the user's.

Why it helps the product, not just one user

It makes the Design System more valuable (more places it takes effect) without competing with the design work Claude does for you. It is the kind of personalization users ask for, delivered through a channel you already built and already trust.