Replace Xournal++ with Signed for signing PDFs (#14999)

Signed, Omacom's PDF signing app, takes Xournal++'s place in the base
install and the preinstall set, so Remove and Install Preinstalls cover
it too. A migration installs it on existing machines, unless their owner
has removed the preinstalls; Xournal++ stays on machines that already
have it. The Filling out PDFs chapter now walks through Signed, the GUIs
chapter introduces it, the setup tip points to it, and the unused
Xournal++ config is gone.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

manual/22-guis.md

@@ -69,6 +69,12 @@ You start LibreOffice via the application launcher (`Super + Space`).
 
 You start Hype via the application launcher (`Super + Space`). Press `?` inside it to see every shortcut.
 
+## Signed
+
+[Signed](https://github.com/omacom/signed) is Omarchy's own dead-simple way to sign PDFs and fill them in. Put your saved signature, text, and today's date anywhere on a page, then save a signed copy beside the original. See [Filling out PDFs](27-filling-out-pdfs.md) for how.
+
+You start Signed via the application launcher (`Super + Space`), or open a PDF with it from the file manager.
+
 ## Omacalc
 
 [Omacalc](https://github.com/omacom-io/omacalc) is Omarchy's own dead-simple calculator, which opens in a floating window.

manual/27-filling-out-pdfs.md

@@ -2,8 +2,10 @@
 
 Omarchy ships with a nice, basic PDF viewer called Document Viewer. This is the program that'll open any PDFs you just double click on.
 
-But you can only use Document Viewer to fill out PDFs that have been setup as forms. If you need to fill out PDFs that haven't, or you need to sign a PDF, you'll have to right-click the file, select _Open With..._, and pick Xournal++.
+But you can only use Document Viewer to fill out PDFs that have been setup as forms. If you need to fill out PDFs that haven't, or you need to sign a PDF, use [Signed](https://github.com/omacom/signed). Start it via the application launcher (`Super + Space`), or right-click the file, select _Open With..._, and pick Signed.
 
-Xournal++ will let you write anywhere on a PDF using the T tool. If you need to sign a document, you'll need an image of your signature, and you can use the Image tool to insert this signature and resize it.
+Press `T` to type text and `D` to put down today's date. Both land where your mouse pointer is. Drag anything to move it, drag its corner to make it bigger or smaller, and double-click text to change it.
 
-When you're done filling out the PDF, use _File > Export as PDF_ to save the final version.
+To sign, you'll need a picture of your signature: a scan, or a well-lit photo of it on white paper. Open the _Signature_ menu (`Shift + S`), choose _Add signature..._, pick the picture, and give it a name. Signed removes the paper and keeps the ink. From then on, `S` puts your signature under the mouse pointer.
+
+When you're done, use _Save signed copy..._ (`Ctrl + S`) to save the filled-out PDF beside the original, which is never changed. Press `?` inside Signed to see every shortcut.