Tokenize wallet/vault/rail + collapse WidgetTile accent map

[rep0x]

What to build

Replace literal palette colors on themed surfaces with semantic tokens, and collapse the WidgetTile accent map to tokens. Tokenize apps/wallet, apps/vault (ProviderAccounts), and WorkspaceRail (bg-amber-500 etc.); replace WidgetTile's per-tile accent map with semantic tokens. Add an in-code comment on the widget iframe sandboxes (src/app/widget/*) explaining the opaque-origin exception where literal colors are genuinely required.

Acceptance criteria

• wallet / vault / WorkspaceRail use semantic tokens — no raw palette classes
• WidgetTile accent map collapsed to semantic tokens
• Documented in-code comment on src/app/widget/* explaining the literal-color exception
• Build + visual check: wallet, vault, rail

Blocked by

• Wave 2 — fonts + login-accent rollout across all consumers (ui ^0.4.0 / core ^0.5.0) ui#20 (Wave 2 fonts/accent)