Feature/Chore: Replaces all usages of ImageMagik's convert binary with a simple Pillow based helper

This removes ImageMagik as a dependency entirly and all documentation is cleaned up from it.
We no longer need to install it, have a policy for it to allow PDFs and no longer shell
out to it either.

docs/setup.md

@@ -177,7 +177,6 @@ to a positive number to enable polling and disable native filesystem notificatio
     - `pkg-config` for mysqlclient (python dependency)
     - `fonts-liberation` for generating thumbnails for plain text
       files
-    - `imagemagick` >= 6 for image alpha handling
     - `gnupg` for decrypting GPG-encrypted email
     - `libpq-dev` for PostgreSQL
     - `libmagic-dev` for mime type detection
@@ -187,7 +186,7 @@ to a positive number to enable polling and disable native filesystem notificatio
     Use this list for your preferred package management:
 
     ```
-    python3 python3-pip python3-dev imagemagick fonts-liberation gnupg libpq-dev default-libmysqlclient-dev pkg-config libmagic-dev poppler-utils
+    python3 python3-pip python3-dev fonts-liberation gnupg libpq-dev default-libmysqlclient-dev pkg-config libmagic-dev poppler-utils
     ```
 
     These dependencies are required for OCRmyPDF, which is used for text
@@ -416,13 +415,6 @@ to a positive number to enable polling and disable native filesystem notificatio
         You may need to change the path in the files. Example:
         `ExecStart=/opt/paperless/.local/bin/celery --app paperless worker --loglevel INFO`
 
-12. Harden ImageMagick by disabling formats that Paperless-ngx does not use.
-    PDF processing is not needed and should stay disabled.
-
-    Configure the active ImageMagick policy file (commonly
-    `/etc/ImageMagick-6/policy.xml` or `/etc/ImageMagick-7/policy.xml`) and
-    adjust similar to [the docker policy file](https://raw.githubusercontent.com/paperless-ngx/paperless-ngx/refs/heads/main/docker/rootfs/etc/ImageMagick-6/paperless-policy.xml). You should also include restrictions as noted there.
-
 **Optional: Install the [jbig2enc](https://ocrmypdf.readthedocs.io/en/latest/jbig2.html) encoder.**
 This will reduce the size of generated PDF documents. You'll most likely need to compile this yourself, because this
 software has been patented until around 2017 and binary packages are not available for most distributions.