Cleanup files, add comments

ansible/plays/apt-up.yml

@@ -1,5 +1,5 @@
 ---
-- hosts: core
+- hosts: nginx-server
   become: yes
   tasks:
     - name: Ensure package lists are up-to-date

ansible/plays/bookstack-backup.yml

@@ -1,5 +1,5 @@
 ---
-- hosts: bookstack
+- hosts: docker-host
   become: yes
   tasks:
     - name: Create backup directory if it doesn't exist

ansible/plays/hexo-backup.yml

@@ -1,5 +1,5 @@
 ---
-- hosts: hexo
+- hosts: dev
   become: yes
   tasks:
     - name: Backup Hexo files

ansible/plays/hexo-install.yml

@@ -1,6 +1,6 @@
 ---
 - name: Install Hexo static site generator
-  hosts: hexo
+  hosts: dev
   become: yes
   tasks:
     - name: Update apt sources and install npm