feat(widget)!: enforce single source of truth for fee/order/slippage/referrer

[chybisov]

Which Linear task is linked to this PR?

EMB-389 — Wave 1, item #3

Why was it implemented this way?

Today four settings exist in two places — top-level WidgetConfig and sdkConfig.routeOptions — with inconsistent precedence between read paths:

Setting	Top-level	sdkConfig.routeOptions	Read-path precedence
fee	WidgetConfig.fee	routeOptions.fee (via spread)	feeConfig?.fee || fee
referrer	WidgetConfig.referrer	routeOptions.referrer	spread order
routePriority	WidgetConfig.routePriority	routeOptions.order	inconsistent — nested wins in SDKClientProvider, top-level wins in useSettingsActions
slippage	WidgetConfig.slippage	routeOptions.slippage	spread order

Setting both desyncs the SDK client from the settings UI.

This PR makes duplication impossible at the type level by extending the existing Omit in WidgetSDKConfig.routeOptions to also strip fee | referrer | order | slippage. This applies the same rule the codebase already follows for bridges and exchanges.

Additionally drops the top-level WidgetConfig.fee so feeConfig.fee is the single way to set the integrator fee.

Alternatives considered:

• Keep both, document precedence — does not prevent the bug from recurring.
• Move everything to sdkConfig.routeOptions — these are user-configurable defaults that flow into the settings store/UI, conceptually closer to appearance/fromChain than to apiUrl. Top-level is the right home.

Visual showcase

N/A — backend API type changes; widget renders identically. Smoke test confirms the playground loads with no new console errors.

Checklist before requesting a review

• I have performed a self-review and testing of my code.
• This pull request is focused and addresses a single problem.
• If this PR modifies the Widget API or adds new features that require documentation, I have updated the documentation in the public-docs repository.

Breaking change

Migration:
```diff

• fee: 0.01,

• feeConfig: { fee: 0.01 },

• sdkConfig: { routeOptions: { fee: 0.01 } }

• feeConfig: { fee: 0.01 }

• sdkConfig: { routeOptions: { order: 'FASTEST' } }

• routePriority: 'FASTEST'

• sdkConfig: { routeOptions: { slippage: 0.005 } }

• slippage: 0.005

• sdkConfig: { routeOptions: { referrer: '0x...' } }

• referrer: '0x...'
  ```

[github-actions]

E2E Examples — failures

The following example(s) failed:

• nft-checkout
• vite-iframe-wagmi

See the workflow run for Playwright reports and logs.