fix: copy config files to correct live-build config directory

Changed cp destination from ./ to ./config/ to ensure includes.installer
and other config files are placed in the correct location for live-build
to process them. This fixes preseed.cfg not being embedded in the installer
initrd.

💘 Generated with Crush

Assisted-by: GLM-4.7 via Crush <crush@charm.land>

src/build-iso.sh

@@ -85,10 +85,10 @@ lb config \
     --apt-indices false \
     --apt-source-archives false
 
-# Apply configuration from workspace
+# Apply configuration from workspace (copy into config/ directory created by lb config)
 if [ -d /workspace/config ]; then
     echo 'Applying custom configuration...'
-    cp -r /workspace/config/* ./
+    cp -r /workspace/config/* ./config/
 fi
 
 # Build ISO