docs: fix broken links and anchors across documentation

Fix ~30 broken links and anchors across the documentation site, including
incorrect relative paths, mismatched anchor names, zero-width characters
in URLs, and references to renamed or removed headings.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Fredrik Adelöw <freben@spotify.com>

docs/getting-started/homepage.md

@@ -26,7 +26,7 @@ At the end of this tutorial, you can expect:
 
 Before we begin, make sure
 
-- You have created your own standalone Backstage app using [`@backstage/create-app`](./index.md#1-create-your-backstage-app) and not using a fork of the [backstage](https://github.com/backstage/backstage) repository.
+- You have created your own standalone Backstage app using [`@backstage/create-app`](./index.md#creating-and-running-a-backstage-application) and not using a fork of the [backstage](https://github.com/backstage/backstage) repository.
 - You do not have an existing homepage, and by default you are redirected to Software Catalog when you open Backstage.
 
 Now, let's get started by installing the home plugin and creating a simple homepage for your Backstage app.