chore: Move the changelog to the repository root

The release notes rendered in the about modal only existed as an asset
inside the client, where nothing outside a build would look for them. The
file moves to CHANGELOG.md at the root and the about modal reads it from
there, so the client build and the Docker image copy in the same file the
repository keeps.

An unreleased section collects the orphaned reference fixes and the
pagination fixes.

client/src/components/common/AboutModal/AboutPane.jsx

@@ -11,7 +11,7 @@ import version from '../../../version';
 import Markdown from '../Markdown';
 
 import aboutLogo from '../../../assets/images/about-logo.png';
-import whatsNewUrl from '../../../assets/docs/whats-new.md?url';
+import changelogUrl from '../../../../../CHANGELOG.md?url';
 
 import styles from './AboutPane.module.scss';
 
@@ -23,7 +23,7 @@ const AboutPane = React.memo(() => {
     async function fetchWhatsNew() {
       let response;
       try {
-        response = await fetch(whatsNewUrl);
+        response = await fetch(changelogUrl);
       } catch {
         return;
       }