Register of interest page layout

[lucascumsille]

Fixes: #2015

The following changes have been made:

• Register of interest page uses the same layout as the MP page. So we don't have two different styles that at the same cover similar layout out content.
• Move the styling from in-page-nav to its own stylesheet. So we can reuse it in other pages.
• Added a component .js-table-of-content-markdown that creates from the markdown a table of content with the proper classes so it can use the current functionality/styles of js-table-of-content
• Added a newsletter and donation prompts to the sidebar, just like in the MP. Because the copy is different I decided to create new templates instead of all using the current templates.

Note: the odd styling inside the newsletter should be fixes when merging [this previous PR needs](https://github.com//pull/2020)

[ajparsons]

So mostly looks good!

• This will need a bit of changing after merging my changes to the other PR - as that changes the approach for specifying something as a newsletter page.
• The static page donation/newsletter bubble are fairly similar to the ones in the MP page - I wonder about moving the display bit to sidebar/_donation.php etc - and then include that after loading the specific data for each location?

[lucascumsille]

The static page donation/newsletter bubble are fairly similar to the ones in the MP page - I wonder about moving the display bit to sidebar/_donation.php etc - and then include that after loading the specific data for each location?

Just to clarify the styling is the same, however the content/copy is different. I'm happy to go with this approach if we can have different content in the MP and Register of Interest.

This will need a bit of changing after merging my changes to the other PR - as that changes the approach for specifying something as a newsletter page.

Perfect I'll rebase this one with master once we have merge this PR and make the changes.

[lucascumsille]

@ajparsons I just added two commits that follows the same logic for the announcements in the MP page.

I also included some commits to:

• Keep the announcements from disappearing on mobile, instead they'll stack.
  https://github.com/user-attachments/assets/e47bb3a8-15ef-4ff4-8960-95f51d1702ba

• I noticed we had a bug for the reusability of the announcements where the variables defined at the very top of donation and newsletter keep overriding what I had in the sidebar.php for static pages.

[lucascumsille]

@ajparsons I think this should be ready for review:
JSON Example:

  {
    "title": "Support TheyWorkForYou",
    "content": "We are a charity - donate today to invest in making UK politics more transparent and accessible. <br> ♥️ Even £5 goes a long way!",
    "url": "https://www.mysociety.org/donate/",
    "button_text": "Donate now",
    "button_class": "button--negative",
    "location": ["sidebar_interests"],
    "type": "donation",
    "weight": 2,
    "published": true,
    "lang": "en",
    "start_time": "2025-01-01T00:00:00",
    "end_time": "2030-12-31T23:59:59"
  },
{
  "title": "Find out what else we do",
  "content": "Subscribe to our newsletter",
  "thumbnail_image_url": "https://www.mysociety.org/files/2026/03/wdtk-image-event.jpg",
  "thumbnail_image_alt_text": "",
  "url": "https://www.mysociety.org/subscribe/",
  "button_text": "Subscribe",
  "button_class": "button--primary",
  "location": ["sidebar_interests"],
  "type": "newsletter",  
  "footer_html": "<a href=\"https://www.mysociety.org/privacy#newsletter\">Your data and how we use it</a>",
  "weight": 3,
  "published": true,
  "lang": "en",
  "start_time": "2025-01-01T00:00:00",
  "end_time": "2030-12-31T23:59:59"
}