docs: Remove the non-existent /node/{node}/canvas/default route from the README

Problem/Motivation

The README's Routes table documents a /node/{node}/canvas/default path ("Edit the shared ContentTemplate default layout"), but the module does not define any such route. canvas_override.routing.yml only defines /node/{node}/canvas, /node/{node}/canvas/reset and the POST-only /node/{node}/canvas/reset/confirm HTMX endpoint. Visiting /node/{node}/canvas/default returns a 404, even as an administrator.

Editing the shared default layout is actually reached through Canvas's own Edit template local task (entity.node.template), whose visibility Canvas Override already gates with the edit canvas default template permissions in CanvasOverrideHooks::menuLocalTasksAlter().

Steps to reproduce

• Install canvas_override 1.0.x on Drupal 11.4.5 with Canvas 1.10.1 (with the #3567225 patch) and enable it on a content type.
• As user 1, visit /node/{nid}/canvas/default for a node of that type.
• Result: 404. Confirmed with Playwright browser testing on plain Drupal core 11.4.5 and Drupal CMS 2.0.

Proposed resolution

Remove the /node/{node}/canvas/default row from the README's Routes table and describe the real path: the Edit template tab provided by Canvas, gated by the edit canvas default template / edit canvas default template for {type} permissions.

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 the README Routes table: removed the non-existent /node/{node}/canvas/default route and documented the Edit template tab instead.