[P2] selectors: extract passkey 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

4 selectors (`getIsPasskeyRegistered`, `getPasskeyDerivationMethod`, `getIsEnrolledPasskeyIncompatibleWithSidepanel`, `getIsPasskeyFeatureAvailable`) — external `shared/lib/passkey` + `getIsSocialLoginFlow` only. `passkey.test.ts` already exists.

## Solution

Create `ui/selectors/passkey.ts`.

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

- [ ] `passkey.ts`; imports repointed directly to the module (no barrel); pairs with existing test. Tests green.

Start with ui/selectors/selectors.js and the four passkey selectors listed in the issue, then inspect the existing passkey.test.ts. Create ui/selectors/passkey.ts, repoint importing sites directly to that module without a barrel, and remove the selectors from selectors.js. Run the passkey test and the relevant test suite to confirm all tests are green.

Written by the indexing model from the issue text.