Site Migration flows should redirect to home instead of /start

[escapemanuele]

Related to https://github.com/Automattic/dotcom-forge/issues/9709#issuecomment-2488150145

Proposed Changes

Instead of redirecting the users to /start, when there is not site id or site slug, we redirect them to /home as it is done in the site-setup flow

Why are these changes being made?

When you remove the siteSlug/siteId in the /setup/site-setup steps, you get redirected to the primary site. However, when you remove the siteSlug/siteId in the /setup/site-migration/site-migration-identify step, you get redirected to the Domains step, and potentially create a new site if you continue the flow.

Testing Instructions

• Go through onboarding (/start)
• After domains and plans, select "Import existing content or website"
• Try to remove the site slug from the url
• You should land in /home

[github-actions[bot]]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-125213

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-125213&env=jetpack

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https://calypso.live?image=registry.a8c.com/calypso/app:build-125213&env=a8c-for-agencies

[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

Sections (~10 bytes removed 📉 [gzipped])

``` name parsed_size gzip_size site-migration-flow -57 B (-0.1%) -10 B (-0.1%) hosted-site-migration-flow -57 B (-0.1%) -10 B (-0.1%) ``` Sections contain code specific for a given set of routes. Is downloaded and parsed only when a particular route is navigated to.

Legend

What is parsed and gzip size?

**Parsed Size:** Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory. **Gzip Size:** Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.

[matticbot]

This PR modifies the release build for the following Calypso Apps:

For info about this notification, see here: PCYsg-OT6-p2

• notifications
• wpcom-block-editor

To test WordPress.com changes, run install-plugin.sh $pluginSlug fix-site-migration-redirection on your sandbox.