feat: add block-based footer menu using StreamField (refs #554)

[Raghaddahi]

This PR adds a footer menu to the demo in addition to the existing footer text.

The footer menu adds a second level to the footer, consisting of sections where each section has a list of menu items and each menu item can be a link to a page, url or document.

Changes

• Add the footer menu before the footer text and social media links
• Followed the same block structure added in issue comment

Features

• Overriding pages' titles to use text that is better suited as menu item labels
• Reordering menu items without changing the order of the page
• External links and document links in menus
• Settings preview (PreviewableMixin)

Testing

Tested by adding external URL, pages and document in the admin dashboard.

Before

After

AI Usage

Used Claude.ai to understand the existing codebase (FooterText model, navigation_tags.py) and to assist in writing footer_menu.html template. All code was reviewed by me.

Note

I implemented the footer menu first as mentioned in the issue. The main menu refactor I will refactor the main menu once I discus it with the team.

[Raghaddahi]

Hey @thibaudcolas, would love to get your review on this PR

[Raghaddahi]

hey @cnk, could you pls rerun the workflows, i have fixed the failing one.