fix(docs): broken Preview tool link returns 404 in troubleshooting guide

[ygd58]

Bug

The troubleshooting guide links to https://base.dev/preview which returns 404.

Steps to reproduce:

1. Visit https://docs.base.org/apps/troubleshooting/common-issues
2. Click the 'Preview tool' link
3. Gets 404 error

Root cause:
The Preview tool URL changed from /preview to /apps/preview:

• ❌ https://base.dev/preview → 404
• ✅ https://base.dev/apps/preview → 200

Affected file:
docs/apps/troubleshooting/common-issues.mdx lines 32 and 62

I'd be happy to open a PR for this fix.