fix: Guard the reset HTMX URL generation in menuLocalTasksAlter against RouteNotFoundException

Problem/Motivation

CanvasOverrideHooks::menuLocalTasksAlter() generates a URL for the POST-only HTMX endpoint canvas_override.node.canvas.reset.do (via Url::toString()) to wire the Reset tab's hx-post attribute. When that route is not (yet) in the router table, Symfony\Component\Routing\Exception\RouteNotFoundException escapes the hook and takes down every page that renders local tasks with an HTTP 500.

This is not hypothetical: any Drupal core or Drupal CMS site running an earlier canvas_override release (1.0.0-beta3 or older, which predates the reset HTMX route) hits it on update. A composer update deployed before the cache/router rebuild runs — the normal ordering for containerized deploys — leaves a window where every node page 500s with:

Symfony\Component\Routing\Exception\RouteNotFoundException: Route "canvas_override.node.canvas.reset.do" does not exist.
    Drupal\canvas_override\Hook\CanvasOverrideHooks->menuLocalTasksAlter()
    Drupal\Core\Menu\LocalTaskManager->getLocalTasks()
    Drupal\navigation\NavigationRenderer->getLocalTasks() …

A missing route for a decorative enhancement (the HTMX confirm shortcut; the tab's href still points at the standalone confirm form) should degrade gracefully, not fatal the site.

Steps to reproduce

• Install canvas_override 1.0.0-beta3 on a Drupal 11.4 site (plain core or Drupal CMS) and enable it.
• Replace the module code with 1.0.x HEAD (as composer would on deploy) without rebuilding caches.
• Visit any node page as an authenticated user with local tasks: HTTP 500 with the trace above, on every page, until drush cr.

Proposed resolution

Wrap the reset-endpoint URL generation in a try/catch for RouteNotFoundException and skip the HTMX wiring when the route is unavailable — the tab keeps its normal href to the confirm form, and the site keeps rendering.

Remaining tasks

• ✅ File an issue about this project
• ✅ Addition/Change/Update/Fix to this project
• ✅ Testing to ensure no regression
• ✅ Automated unit/functional testing coverage
• ➖ Developer Documentation support on feature change/addition
• ➖ User Guide Documentation support on feature change/addition
• ➖ UX/UI designer responsibilities
• ➖ Accessibility and Readability
• ✅ Reviewed by a human
• ✅ Code review by maintainers
• ✅ Full testing and approval
• ✅ Credit contributors
• ✅ Review with the product owner
• ✅ Update Release Notes
• ✅ Release canvas_override-1.0.0

User interface changes

• N/A

API changes

• N/A

Data model changes

• N/A

Release notes snippet

• Fixed a site-wide 500 (RouteNotFoundException) on pages with local tasks when the reset HTMX route is missing from the router, e.g. during a code update before caches are rebuilt.