Fix wallet nested-asset contrast

[twblack88]

Context

When a user expands a portfolio asset, the nested/underlying asset rows sit on bg-whiteAlpha-50 (#ffffff0a) — nearly invisible against the parent surface. They need a visible background step-up and a structural nesting cue.

Example

Files

• apps/agentic-chat/src/components/ui/DrawerListItem.tsx:18-22 — parent asset row (bg-whiteAlpha-50)
• apps/agentic-chat/src/components/Portfolio/GroupedAssetRow.tsx — RelatedAssetsList rendering nested rows

Approach

• Bump nested asset background from bg-whiteAlpha-50 → bg-whiteAlpha-100 or bg-whiteAlpha-200 so they sit visibly above the parent surface.
• Consider adding a subtle left-border / indent treatment on nested rows so the nesting reads structurally, not just by indentation.

Verification

bun run lint
bun run type-check
bun test

Visual QA: open a portfolio asset with nested underlying assets; nested rows should be clearly distinguishable from the parent row using different gray from the design system.