Remove buildwithfern.com hyperlink from logo in all templates

[kgowru]

Summary

Removes the href: https://buildwithfern.com from the logo configuration in all three template docs.yml files (classic, minimal, products). This makes the logo in the top-left corner of template docs sites non-clickable, rather than linking to buildwithfern.com.

Review & Testing Checklist for Human

• Confirm that removing the logo href entirely (rather than replacing it with a different URL) is the desired behavior
• After merging, verify by creating a new docs site from a template (e.g. via the Postman collection flow) and confirming the logo is no longer a link

Notes

• All three templates had the identical href: https://buildwithfern.com line; all three were updated.
• This only affects newly created docs sites from these templates. Existing sites that were already published from these templates will not be affected.

Link to Devin session: https://app.devin.ai/sessions/f3fc610167e842f18ba217f8ba4de2e1
Requested by: @kgowru

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