[openstreetmap/openstreetmap-website] Show tag changes in object history view (PR #6448)

[Ian Dees]

### Description

This adds highlighting of tag changes in each version to the history view for primitives:
- Tags that are **new** will be highlighted in green
- Tags that have **changed value** will be highlighted in yellow, with the value change described using an arrow like `old → new`
- Tags that have been **removed** will be highlighted in red, with the value `deleted`

Screenshot:
<img width="839" height="494" alt="image" src="https://github.com/user-attachments/assets/f6a066c5-84bb-4c84-b3fa-469238da6be8" />

This probably closes https://github.com/openstreetmap/openstreetmap-website/issues/738. I know there are other discussions and tickets related to this idea, but I couldn't find them in my few searches.

Ruby is not my native language, so please point out where I can improve the change.

### How has this been tested?

I ran the site locally in Docker, added some fake data to the database, and inspected it on my browser locally.

You can view, comment on, or merge this pull request online at:

  https://github.com/openstreetmap/openstreetmap-website/pull/6448

-- Commit Summary --

  * Show tag changes in object history view

-- File Changes --

    M app/assets/stylesheets/common.scss (39)
    M app/helpers/browse_helper.rb (61)
    M app/views/browse/_common_details.html.erb (6)
    A app/views/browse/_tag_details_with_changes.html.erb (18)
    A app/views/browse/_tag_with_changes.html.erb (5)

-- Patch Links --

https://github.com/openstreetmap/openstreetmap-website/pull/6448.patch
https://github.com/openstreetmap/openstreetmap-website/pull/6448.diff

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