feat: dollar tokens Phase 3 foundation (stacked on PR #148)

[TuCopFi]

Summary

Foundation layer of Phase 3 of the dollar-tokens initiative. Lands the pure planner, multi-quote hook, Redux slice for in-flight state, orchestrator saga, selectors, and a planner-input hook. No UI integration in this PR; UI bolts on in a follow-up.

Stacked on top of PR #148 (Phase 1 + Phase 2 data layer + cards). Once #148 merges to Development, the base of this PR will become Development.

Spec: `tasks/plans/dollar-tokens-phase3-spend-order.md` (local-only).
Implementation plan: `tasks/plans/dollar-tokens-phase3-foundation-implementation.md` (local-only).

What this PR contains

New module `src/dollarsSpend/`:

• types.ts - SpendStep, MultiSwapPlan, DollarTokenBalanceSnapshot, SPEND_ORDER (USAT > USDm > USDC > USDT), DOLARES_VIRTUAL_TOKEN_ID
• planSpend.ts - pure planner walking spend order with dust filter (9 unit tests)
• slice.ts - Redux state for in-flight multi-swap (plannedSteps, completedSteps, failedAtIndex, lastError) (8 unit tests)
• useMultiSwapQuote.ts - fetches N Squid quotes in parallel for upfront totals (4 unit tests)
• saga.ts - executeMultiSwapSaga orchestrator: per-step quote refetch + dispatch swapStart + race(swapSuccess/swapError) on swapId. On step failure halts and emits multiSwapStepFailed; on full success emits multiSwapCompleted. (3 saga tests)
• selectors.ts - inFlight, hasInFlight, inFlightProgress (5 unit tests)
• useDollarBalanceSnapshots.ts - builds the planner's input array from the current wallet token state (3 unit tests)
• index.ts - barrel re-exports

Auxiliary:

• src/swap/useSwapQuote.ts - extract `fetchSwapQuote` as a named export for re-use (lightweight price-discovery function; the existing hook keeps its full prepareSwapTransactions flow)
• src/redux/reducersList.ts - register dollarsSpend reducer
• src/redux/sagas.ts - spawn dollarsSpendSaga
• src/redux/migrations.ts - migration 247 seeds the new slice
• src/redux/store.ts - bump persistConfig.version to 247
• test/RootStateSchema.json + test/schemas.ts - regenerated schema, v247Schema added
• knip.ts - ignore the dollarsSpend barrel until Phase 3.2 UI consumes it

Verification

• `yarn build:ts` - pass
• `yarn lint` - pass
• `yarn test` - 374 suites pass, 4029 tests pass, 96 snapshots pass, 0 failures
• `yarn knip --no-gitignore` - dollarsSpend barrel ignored as planned

Known follow-ups for Phase 3.2 (UI integration, separate PR)

• TokenBottomSheet `collapseDollars` prop to render the virtual Dolares row
• SwapScreen + GoldBuyEnterAmount + SendEnterAmount route the virtual tokenId through the planner
• MultiSwapProgressSheet + PartialSuccessSheet UI for in-flight + partial-failure states
• New i18n keys (`dollarsSpend.*`)
• Mainnet QA of the full chain
• One architectural item: the orchestrator saga in this foundation passes `preparedTransactions: []` because the light `fetchSwapQuote` does not build them; Phase 3.2 must either (a) extend fetchSwapQuote to call prepareSwapTransactions per step, or (b) have the UI use the full `useSwapQuote` to prebuild quotes including preparedTransactions for each step and pass them via the action payload. Documented in the spec.

Test plan

• yarn test passes (verified locally before push)
• CI passes
• No regression in single-swap flow (existing swap tests pass and were not modified)
• Reviewer confirms the saga's race+take predicate matches both shapes of swapSuccess/swapError payload (object with swapId or raw swapId string)