[IMP] website: improve Optimize SEO and Page Manager

Modal generic:
- Fix footer overflowing buttons by pushing them to a new line.

Page manager:
- Add an SEO column to easily see which pages have incomplete SEO.
- Add an edit SEO column to navigate to the SEO modal on said page.
- Hide "edit in backend" column as debug.
- Generally improve the whole view by adding appropriate titles on icons, etc.

SEO modal:
- Improve general style.
- Add description length alert.
- Restructure the keyword table/suggestions.
- Reset page meta to their initial value on Discard.
- Various small usability improvements.

PR: #26897
task-1850579