chore(brand): refresh app icons + add brand source artwork

Replaces desktop and web icon binaries with the new brand mark, ships
PNG raster exports under assets/brand/ alongside the existing SVG
sources, adds Alternative Styles artwork variants, and updates the
icon generation script and System Prompt doc. deploy.sh excludes
the new local-only artifacts (*.rtfd, assets/brand, electronbuild.sh,
multi-platform-roadmap.md) so they don't get rsync'd to the live
boxes. Drops ARCHITECTURE_AUDIT.md (obsolete).

deploy.sh

@@ -49,8 +49,12 @@ EXCLUDES=(
   --exclude='outdated trash'
   --exclude='docs/superpowers'
   --exclude='*.rtf'
+  --exclude='*.rtfd'
   --exclude='ARCHITECTURE_AUDIT.md'
   --exclude='Backspace-design-prototype.html'
+  --exclude='assets/brand'
+  --exclude='electronbuild.sh'
+  --exclude='multi-platform-roadmap.md'
 )
 
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