Wallet-wide UI refresh: tokens, unified components, flow restyles — tracking

Tracking issue for a wallet-wide UI refresh: shared design tokens, one button component, consistent selection states, and a flow-by-flow restyle. Each item below is (or will be) its own issue with concrete scope and acceptance criteria; several also fix defects found while auditing that flow.

Order matters for the first three — every flow consumes them. After that, items are independent.

- [ ] Design tokens: CSS custom properties + Tailwind preset, light/dark via `data-theme`
- [ ] One Button: unify the six button implementations, retire outlined secondaries
- [ ] Selection states: one treatment per container (list rows, grouped rows, cards)
- [ ] Home: fixed-size balance card, one notice component, token detail restyle
- [ ] Onboarding: 4-step flow with deferrable seed backup, forgot-passcode, sign-out ladder
- [ ] Send (same-chain): recipient, scanner, amount, review — includes the devnet QR prefix fix
- [ ] Send (cross-chain): network by name, route selection on the send screen
- [ ] Contacts: swipe actions, native delete confirm, add the missing `updateContact`
- [ ] Receive: share-only layout, touch-visible copy feedback
- [ ] Swap: restyle + loading state on submit (button currently shows nothing while submitting)
- [ ] Activity: list states, surface failed transactions, pending notes under Activity
- [ ] Settings: render the built-but-hidden currency picker, dApps empty state, change passcode
- [ ] Security & recovery: wire the app-lock toggle, fix blank screens, reveal flows
- [ ] dApp browser: consent UI for all request types on mobile
- [ ] Global states: lock, connectivity, camera chrome, theme-proof QR rendering

Mockups for every screen (both themes) exist and will be attached per issue as each one is opened.