Refine packaging layout and Arch build paths

* Move Arch-specific ignore rules into `packaging/arch/.gitignore` and simplify top-level `.gitignore`/`.dockerignore`.
* Update Arch `PKGBUILD` to sync from the project root and drop `packaging/` from the installed tree.
* Fix OS-specific `package.sh` helpers to resolve the new `packaging/*` locations correctly for Arch, Debian/Ubuntu, Fedora, and CentOS.

packaging/arch/PKGBUILD

@@ -15,7 +15,7 @@ makedepends=('rsync')
 install=${pkgname}.install
 
 # Local source checkout — avoids the tarball requirement.
-# This assumes you build the package from inside the main project repository.
+# We build from the project root (two levels above packaging/arch/).
 source=()
 sha256sums=()
 
@@ -24,12 +24,17 @@ _srcdir_name="source"
 
 prepare() {
   mkdir -p "$srcdir/$_srcdir_name"
+
+  local project_root
+  project_root="$(cd "$startdir/../.." && pwd)"
+
   rsync -a \
     --exclude=".git" \
     --exclude=".github" \
     --exclude="pkg" \
     --exclude="srcpkg" \
-    "$startdir/" "$srcdir/$_srcdir_name/"
+    --exclude="packaging" \
+    "$project_root/" "$srcdir/$_srcdir_name/"
 }
 
 build() {
@@ -62,7 +67,8 @@ package() {
     "$pkgdir/usr/lib/package-manager/PKGBUILD" \
     "$pkgdir/usr/lib/package-manager/Dockerfile" \
     "$pkgdir/usr/lib/package-manager/debian" \
+    "$pkgdir/usr/lib/package-manager/packaging" \
     "$pkgdir/usr/lib/package-manager/.gitignore" \
     "$pkgdir/usr/lib/package-manager/__pycache__" \
-    "$pkgdir/usr/lib/package-manager/.gitkeep"
+    "$pkgdir/usr/lib/package-manager/.gitkeep" || true
 }