fix(snap): import findSnap into useDragElements (snap threw at runtime)

`e9a5cc8e` extracted the snap math to `snap.ts` and *re-exported* `findSnap`
(`export { findSnap } from './snap'`) but never imported it for local use, while
`applySnap` calls it. A re-export creates no local binding, so every drag that
reached `applySnap` threw `ReferenceError: findSnap is not defined` — snap-to
guides were silently broken in the dev editor. Add `findSnap` to the local import
(the re-export stays for external callers). Surfaced by the rewritten v-drag E2E.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: ryan-williams

packages/client/composables/useDragElements.ts

@@ -9,7 +9,7 @@ import { directiveInject } from '../utils'
 // `getVisibleBounds`, `findSnap`, `SNAP_THRESHOLD` moved to `./snap.ts` so the
 // snap math is unit-testable without a Vue runtime / vite virtual modules.
 // Re-exported below for callers that already import them from this module.
-import { getVisibleBounds } from './snap'
+import { findSnap, getVisibleBounds } from './snap'
 import {
   discardTopMatching,
   beginEdit as historyBeginEdit,