chore: Prep work for migrating to Tailwind v4 (#45285)

This PR preps the monorepo for a migration to Tailwind v4:
- Bump all Tailwind dependencies and libraries to the latest possible
version, while still compatible with Tailwind 3.
- Cleans up obsolete Tailwind 3 specific options and configs.
- Cleans up unused CSS files and fixes the CSS imports.
- Migrates all `important` uses in `@apply` lines to using the `!`
prefix.
- Move `typography.css` to the `config` package and import it from the
apps.
- Migrated all occurrences of `flex-grow`, `flex-shrink`,
`overflow-clip` and `overflow-ellipsis` since they're deprecated and
will be removed in Tailwind 4.
- Make the default theme object typesafe in the `ui` package.
- Migrate all `bg-opacity`, `border-opacity`, `ring-opacity` and
`divider-opacity` to the new format where they're declared as part of
the property color.
- Bump and unify all imports of `postcss` dependency.

apps/docs/package.json

@@ -158,7 +158,7 @@
     "globby": "^13.2.2",
     "graphiql": "^4.0.2",
     "openapi-types": "^12.1.3",
-    "postcss": "^8.5.3",
+    "postcss": "catalog:",
     "shiki": "^3.2.1",
     "shx": "^0.4.0",
     "simple-git": "^3.24.0",