docs: Replace Debian with Mobian when it's about Mobian

Mobian is a Debian *derivative*, not 'unofficial' Debian.
Debian is Debian. Mobian is Mobian.

Therefor use the Mobian logo when it's about Mobian and (slightly)
update the text and URLs to reflect the difference.

content/documentation/PinePhone/Software/Releases.adoc

@@ -230,11 +230,10 @@ The installation of the stable images is strongly suggested. The dev images migh
 
 === Mobian
 
-{{< figure src="/documentation/images/Debian-logo.png" width="100" >}}
+{{< figure src="/documentation/images/Mobian-logo.png" width="100" >}}
 
-An unofficial https://www.debian.org[Debian] build for ARM64 running with Phosh (developed by Purism, uses Wayland instead of Xorg).
-The base system is pure Debian, with only the GUI applications and a few others (ModemManager, WiFi chip firmware) being built from modified sources (as well as the kernel and u-boot).
-Current version is Debian Bookworm.
+A https://www.mobian.org[Mobian] build for ARM64 running with Phosh (developed by Purism, uses Wayland instead of Xorg).
+The current version of the base Debian system is Debian Bookworm. Only the GUI applications and a few others (ModemManager, WiFi chip firmware) are built from modified sources (as well as the kernel and u-boot).
 
 ==== Download
 

content/documentation/PinePhone_Pro/Software/Releases.adoc

@@ -138,9 +138,9 @@ Manjaro is a user-friendly Linux distribution based on the independently develop
 
 == Mobian
 
-{{< figure src="/documentation/images/Debian-logo.png" width="100" >}}
+{{< figure src="/documentation/images/Mobian-logo.png" width="100" >}}
 
-An unofficial https://www.debian.org[Debian] build for ARM64 running with Phosh. The current version of the base Debian system is Debian Bookworm. See the installation instructions https://wiki.debian.org/InstallingDebianOn/PINE64/PinePhonePro[here]. If you have questions about Mobian, please ask them in the https://matrix.to/#/#mobian:matrix.org[Mobian Matrix room].
+A https://www.mobian.org[Mobian] build for ARM64 running with Phosh. The current version of the base Debian system is Debian Bookworm. See the installation instructions https://wiki.debian.org/InstallingDebianOn/PINE64/PinePhonePro[here]. If you have questions about Mobian, please ask them in the https://matrix.to/#/#mobian:matrix.org[Mobian Matrix room].
 
 === Download
 

content/documentation/PineTab/Operating_systems.adoc

@@ -36,9 +36,9 @@ Both Beta releases and weekly unstable builds for Phosh and Plasma Mobile can be
 
 == Mobian
 
-{{< figure src="/documentation/images/Debian-logo.png" width="100" >}}
+{{< figure src="/documentation/images/Mobian-logo.png" width="100" >}}
 
-*Mobian* is an unofficial https://www.debian.org[Debian] build for ARM64 running with Phosh. The current version of the base Debian system is Debian Bookworm. See the installation instructions https://wiki.debian.org/InstallingDebianOn/PINE64/PineTab[here]. If you have questions about Mobian, please ask them in the https://matrix.to/#/#mobian:matrix.org[Mobian Matrix room].
+A https://www.mobian.org[Mobian] build for ARM64 running with Phosh. The current version of the base Debian system is Debian Bookworm. See the installation instructions https://wiki.debian.org/InstallingDebianOn/PINE64/PineTab[here]. If you have questions about Mobian, please ask them in the https://matrix.to/#/#mobian:matrix.org[Mobian Matrix room].
 
 Download: