Hoist OrderbookDepth icon components to module scope

[plind-junior]

Why

BtcIcon, TaoIcon, and AssetIcon are declared inside OrderbookDepth (src/components/dashboard/OrderbookDepth.tsx:29-84). Every parent render creates new component types, so React unmounts and remounts the SVG subtrees.

Not a user-visible bug today — the icons are stateless SVGs, so the remount is invisible. But it violates React's "don't define components inside components" guidance and becomes a real bug if the icons ever gain state, refs, animations, or lazy children.

Fix

Hoist to module scope; each icon calls useTheme() internally. No prop threading, no React.memo.

Acceptance

• Icons at module scope.
• Colors read via useTheme() inside each icon.
• Visual output unchanged (light + dark).
• tsc --noEmit + lint pass.

[wmagev]

Can I tackle this too?

[plind-junior]

Sure, go ahead. Appreciate your enthusiasm