fix(docs): address CTO review feedback on marketing site

- Convert mobile-groomers.html from Markdown to proper HTML
- Fix "Client/p pet profiles" typo → "Client/pet profiles"
- Add missing trailing newlines to all files
- Remove duplicate "Back to Home" link in getting-started/index.html
- Fix link paths: use relative URLs instead of /groombook/docs/ absolute paths
- Remove placeholder testimonials with fake names

Co-Authored-By: Paperclip <noreply@paperclip.ing>

docs/_config.yml

@@ -16,4 +16,4 @@ footer:
     - label: Issues
       url: https://github.com/groombook/groombook/issues
     - label: Discord
-      url: https://discord.gg/groombook
+      url: https://discord.gg/groombook