Wiki UX fixes

[rmehta]

• [x] Home page for docs.frappe.io
• [x] Clear cache when wiki space navbar is updated
• [x] Remove scrolling animation for sidebar
• [x] Remove dark mode switch (use auto]
• [x] Page edit options near title (?)
• [x] 15px for body font? https://frappecloud.com/draft/home

[pranjal-tank]

hello @rmehta I have already raised PR against point 3, can you please review it.

https://github.com/frappe/wiki/pull/248