Merge commit '3f6887557b23d363e7f8f18518db4447739d64bb' into glitch-soc/merge-upstream

Conflicts:
- `app/javascript/entrypoints/common.js`:
  Upstream moved everything from `app/javascript/packs` to
  `app/javascript/entrypoints` while this file was a glitch-soc
  addition. Moved it like the rest.
- `tsconfig.json`:
  Conflict due to glitch-soc's flavor.
  Updated like upstream.

Also moved and updated the following files accordingly:
- `app/javascript/flavours/vanilla/theme.yml`
- `app/javascript/flavours/glitch/theme.yml`
- everything in `app/javascript/flavours/glitch/packs`

app/javascript/flavours/glitch/entrypoints/error.js

@@ -0,0 +1,14 @@
+import '@/entrypoints/public-path';
+import ready from 'flavours/glitch/ready';
+
+ready(() => {
+  const image = document.querySelector('img');
+
+  image.addEventListener('mouseenter', () => {
+    image.src = '/oops.gif';
+  });
+
+  image.addEventListener('mouseleave', () => {
+    image.src = '/oops.png';
+  });
+});