Fix top navigation alignment

[bartaz]

Done

Fixes the alignment of top navigation:

• uses navigation 25/75 split from Vanilla
• updates Vanilla (to fix the navigation wrapping issue)
• removes unnecessary navigation customisations that were causing conflicts between Vanilla, global-nav and local responsive breakpoints

How to QA

• visit home page on demo (https://snapcraft-io-5000.demos.haus/)
• make sure top navigation is well aligned (first item should align with hero content)
• make sure navigation works as expected on all screen sizes
• repeat steps above for documentation (test locally as it's not available on demos)

Testing

• This PR has tests
• No testing required (explain why): visual changes only

Issue / Card

Fixes WD-18308

Screenshots

Before

After

[webteam-app]

Demo

Jenkins

demos.haus