Host the manual's images in the repo under manual/images (#6861)

* Host the manual's images in the repo under manual/images

Replaces all learn.omacom.io/manual.omakub.org hotlinks with local webp
files capped at 1600px wide (~20MB total), so the manual is fully
self-contained. Theme and unlock previews are converted from the
canonical themes/*/preview.png files. A handful of illustration shots
are interim conversions of the current images, pending retakes.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Retake the illustration screenshots fresh at 3x scaling

Navigation, clipboard history, notices, tmux layouts, prompt, and About
reshot on a clean workspace at 3.13x (1920x1080 logical on 6K) across
ten themes: Tokyo Night, Catppuccin, Gruvbox, Kanagawa, Everforest,
Nord, Osaka Jade, Rose Pine, Matte Black, and Ristretto.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Drop the extra themes chapter from the manual

The community theme gallery will live elsewhere. Removes the chapter
and its 114 gallery images, renumbers the following chapters, and
repoints the two references (theme installs still work via
Install > Style > Theme in the menu).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Reference the shipped theme previews instead of copying them

The themes chapter now points straight at themes/*/preview.png and
preview-unlock.png, so previews can never drift from the source and
manual/images drops from 6.3MB to 3.5MB.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

manual/41-branding.md

@@ -12,13 +12,13 @@ omarchy plymouth preview '#1d2021' '#ebdbb2' logo.png preview.png
 
 Then apply the setup with `omarchy plymouth set '#1d2021' '#ebdbb2' logo.png`, which will also give the SDDM login screen the same colors and logo. If you want to revert, you can use `omarchy plymouth reset`.
 
- ![shopify-plymouth.jpeg](https://learn.omacom.io/u/shopify-plymouth-AjqlgW.jpeg)
+ ![branding-plymouth-shopify](images/branding-plymouth-shopify.webp)
 
 ### Screensaver
 
 You can change the logo used for the screensaver under _Style > Screensaver_. It's an ASCII logo, so you can edit the text directly, but you can also hand it a png or svg image, and we'll convert that to ASCII. It looks pretty cool.
 
- ![screensaver.gif](https://learn.omacom.io/u/screensaver-xDOE2Y.gif)
+ ![branding-screensaver](images/branding-screensaver.webp)
 
 There are three entries in that menu:
 
@@ -30,7 +30,7 @@ There are three entries in that menu:
 
 The same three options are under _Style > About_ for the _About_ screen you get from the Omarchy menu, and they work identically — the file is `~/.config/omarchy/branding/about.txt`, and the About window pops up after each change. The About art is converted to a smaller size than the screensaver's, since it has to fit in a window rather than fill your display.
 
- ![about.png](https://learn.omacom.io/u/about-wi4tkl.png)
+ ![branding-about](images/branding-about.webp)
 
 ### Converting images yourself