fix(vue): guard late swipe cancellation - #31515

Issue number: resolves #31514

What is the current behavior?

A cancelled swipe's animation callback can run after navigation has changed. IonRouterOutlet looks up the previous view from the current route and immediately accesses enteringViewItem.ionPageElement. If the view is missing, or its page has been unmounted, cancellation throws a TypeError.

A deterministic reproduction using the real router and outlet is included in the issue: reproduction app. It models a late callback explicitly rather than relying on physical gesture timing. The failure was confirmed in Chrome with the published 9.0.6 packages.

What is the new behavior?

• Return from cancellation cleanup when there is no previous mounted page to hide.
• Preserve the existing aria-hidden and ion-page-hidden cleanup when the page exists, and the completed-swipe navigation behavior.
• Add five regression cases, including late cancellation after returning to the root with the real Ionic router.

Does this introduce a breaking change?

• Yes
• No

Other information

Validation:

• The missing-view and unmounted-page tests fail against the unpatched main-branch bundle with the expected TypeErrors.
• vitest run tests/unit/swipe-cancel.spec.ts tests/unit/router-outlet.spec.ts: 7 tests pass against the locally built patched Vue package.
• npm run typecheck, npm run eslint, and Prettier check for IonRouterOutlet.ts pass in packages/vue.
• npm run bundle passes in packages/vue.

This changes only the cancellation cleanup branch. It does not change navigation semantics or disable swipe gestures.