Changes

• Fixes the StackBlitz and CodeSandbox links in the component and container-with-vitest example READMEs so they point to the correct example folders.
• Adds missing READMEs for the ssr and advanced-routing examples using the same structure as the other example templates, with commands and project details that match each example's actual setup.

Testing

• No test code was added or changed. This PR only updates example README content and link targets.
• Verified the updated sandbox links now match their example directory names and checked the new README content against each example's package.json, astro.config.mjs, and src/ structure.

Docs

• No separate docs repo update is needed because this change only fixes and adds in-repo example READMEs.