feat(buy-sell): align quote card with the DFX web widget

[joshuakrueger-dfx]

Not symptom-driven: proactive redesign requested by JK, phase 2 of aligning the mobile Buy/Sell screens with the DFX web widget (dfx.swiss). Not a reported bug.

Scale: 2 screens (Buy, Sell), affects every user going through the buy/sell flow — this is the primary conversion path of the app.

Smaller fix considered: N/A — this is already scoped down to layout/data-plumbing plus the required state coverage for this phase. Explicitly out of scope for this PR: wallet-switcher bottom sheet, swap icon between buy/sell, hamburger-menu restructuring, and live rate countdown — each is its own follow-up phase.

Summary

• FeeDto (wallet-side type) synced with the backend's actual response shape — it was missing bank, bankFixed, bankVariable, platform, networkStart, so the bank fee was silently unreadable despite being in every API response (verified against ~/DFXswiss/api's fee.dto.ts, not guessed).
• Buy presets fixed to 50/100/250/500 (was 100/500/1000/5000) and moved above the amount input.
• Quote card is now collapsed by default: shield icon + effective rate headline + fee-total badge + chevron toggle, matching the widget's summary-first layout.
• Bank fee row added (uses the now-visible fees.bank).
• "You receive" row gets the accent color.
• Static SEPA payment-method row above the CTA (Buy only — Sell has no payment-method choice at this step).
• CTA now names the target asset plus a trailing arrow icon (PrimaryButton got an additive, optional icon slot).
• Collapsed Buy/Sell quote cards retain visible loading, continue, unsupported, and rejected-quote states; the static payment-method row is no longer presented as an action.

Caught and fixed my own spec mistake before landing: the first pass had the quote-card headline backwards (1 {currency} ≈ {crypto amount} {asset} instead of the widget's 1 {asset} ≈ {price} {currency}). Verified the correct source field (exchangeRate, used directly — not rate, not inverted) against the actual amount/estimatedAmount ratio in the existing test fixtures before landing, not just against the field name.

Test plan

• npm run typecheck — 0 errors
• npm run lint — 0 errors (existing warnings only)
• npm run format — passed
• npx jest --coverage --runInBand — 107/107 suites, 1395/1395 tests; 99.83% lines, 99% floor
• npm run check:matrix — 63 referenced paths, 17 flags, 37 screens
• npm run check:coverage-floor and per-file floors — passed
• visual coverage manifest and self-test — passed; committed buy-amount and sell-no-balance PNGs generated from rendered iOS simulator screens
• iOS release build — passed
• isolated iOS Detox Buy/Sell smoke — 2/2 passed (Buy amount and Sell no-balance); the full-feature authenticated attempt was separately reproduced as an ErrorBoundary Maximum update depth exceeded before Buy/Sell navigation, an existing full-variant simulator/environment blocker outside this diff
• TaprootFreak mechanical gate rerun on the pushed head after every fix commit; current mechanical findings are limited to the external audit advisory and the manually triggered visual/Maestro checks while they run

Final pass (9b586c1):
Coherent: The diff is one Buy/Sell quote-card redesign: shared quote presentation, amount-entry affordances, explicit collapsed error/loading states, and focused screen/E2E/visual coverage; the duplicate locale keys fixed in the final commit are part of that same surface.
Nothing extra: No permanent feature activation, encryption-key changes, real swap implementation, wallet-switcher, menu restructuring, or live-rate countdown was added; those are separate product/security scopes and are explicitly out of this PR.
Sources closed: PR scope and web-widget reference are implemented; all 16 commits were rechecked; the three GitHub review channels and review list are empty; local Jest/typecheck/lint/format/matrix/coverage/visual/build gates passed; the remaining browserslist audit failure is present on develop unchanged and is reported as external.