Better 404s

[Larivact]

• Gitea version (or commit ref): 7f38e2d
• reproducible at https://try.gitea.io/

Description

• UI 404 pages should say something below the 404 image and ideally provide a search box (compare https://try.gitea.io/-404 and https://github.com/404). While using title case in the title is consistent, "Page Not Found" strikes me as odd.
• API 404s currently just return an entirely empty 404 response. Some message and a link to the API documentation would be nice (compare https://try.gitea.io/api/v1/404 and https://api.github.com/notfound).

[jolheiser]

For a search box, what would be different from clicking on the "Explore" tab from the 404 page other than saving 1 click? (Not bashing on click saving, it's important from a UI standpoint of course)

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs during the next 2 weeks. Thank you for your contributions.

[lunny]

This has been fixed by #6077

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs during the next 2 weeks. Thank you for your contributions.