docs: add migrate-v5-experimental-router skill - #2841

Changed pages include:

• index.html - view
• 404.html - view
• api/index.html - view
• data-loaders/index.html - view
• file-based-routing/index.html - view
• guide/index.html - view
• installation.html - view
• introduction.html - view
• zh/index.html - view
• data-loaders/basic/index.html - view

There are more changes not included in the list