[P2] selectors: extract swaps + bridge selectors

**Parent Epic:** [#44566 — `selectors.js` decomposition](https://github.com/MetaMask/metamask-extension/issues/44566)
**Source:** `ui/selectors/selectors.js`
**Size:** S

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## Problem

6 selectors (`getSwapsDefaultToken`, `getIsSwapsChain`, `selectHasBridgeQuotes`, `getIsBridgeChain`, `getIsBridgeEnabled` + private `getBridgeFeatureFlags`). Depends on accounts (`getSelectedAccount`) + multichain + `getUseExternalServices`.

## Solution

Create `ui/selectors/swaps-bridge.ts` (after accounts).

Migration seam (no barrel): repoint every site importing the moved selectors to `ui/selectors/` directly (a `ts-morph` codemod that splits any `../selectors` barrel imports into per-module imports) and delete them from `selectors.js` in the same PR — no re-export facade, per the no-barrel-files convention.

## Acceptance Criteria

- [ ] `swaps-bridge.ts`; imports repointed directly to the module (no barrel). Tests green.

Start with ui/selectors/selectors.js and trace the six swaps and bridge selectors, including the private getBridgeFeatureFlags and their accounts, multichain, and external-services dependencies. Create ui/selectors/swaps-bridge.ts, repoint importing sites directly to that module without a barrel, remove the selectors from selectors.js, and confirm the tests are green.

Written by the indexing model from the issue text.