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

Dockerfile

@@ -6,6 +6,7 @@ RUN pacman -Syu --noconfirm \
         base-devel \
         git \
         nix \
+        rsync \
     && pacman -Scc --noconfirm
 
 # 2) Unprivileged user for building Arch packages
@@ -13,7 +14,7 @@ RUN useradd -m builder
 WORKDIR /build
 
 # 3) Only PKGBUILD rein, um dein Wrapper-Paket zu bauen
-COPY PKGBUILD .
+COPY . .
 
 RUN chown -R builder:builder /build \
     && su builder -c "makepkg -s --noconfirm --clean" \