Fix PKGBUILD source handling and Docker build context

This commit removes unnecessary source entries from PKGBUILD
to allow full local-tree packaging through prepare(), and updates
the Dockerfile to copy the entire repository and install rsync
for makepkg buildtime dependencies.

See conversation: https://chatgpt.com/share/6935db4e-f3e8-800f-b0ca-42f77491ef5b

PKGBUILD

@@ -16,12 +16,8 @@ install=${pkgname}.install
 
 # Local source checkout — avoids the tarball requirement.
 # This assumes you build the package from inside the main project repository.
-source=(
-  "scripts/pkgmgr-wrapper.sh"
-  "scripts/init-nix.sh"
-)
-
-sha256sums=('SKIP' 'SKIP')
+source=()
+sha256sums=()
 
 # Local source directory name under $srcdir
 _srcdir_name="source"