Refactor pkgmgr installers, introduce capability-based execution, and replace manifest layer

References:
- Current ChatGPT conversation: https://chatgpt.com/share/6935d6d7-0ae4-800f-988a-44a50c17ba48
- Extended discussion: https://chatgpt.com/share/6935d734-fd84-800f-9755-290902b8cee8

Summary:
This commit performs a major cleanup and modernization of the installation pipeline:

1. Introduced a new capability-detection subsystem:
   - Capabilities (python-runtime, make-install, nix-flake) are detected per installer/layer.
   - Installers run only when they add new capabilities.
   - Prevents duplicated work such as Python installers running when Nix already provides the runtime.

2. Removed deprecated pkgmgr.yml manifest installer:
   - Dependency resolution is now delegated entirely to real package managers (Nix, pip, make, distro build tools).
   - Simplifies layering and avoids unnecessary recursion.

3. Reworked OS-specific installers:
   - Arch PKGBUILD now uses 'makepkg --syncdeps --cleanbuild --install --noconfirm'.
   - Debian installer now builds proper .deb packages via dpkg-buildpackage + installs them.
   - RPM installer now builds packages using rpmbuild and installs them via rpm.

4. Switched from remote GitHub flakes to local-flake execution:
   - Wrapper now executes: nix run /usr/lib/package-manager#pkgmgr
   - Avoids lock-file write attempts and improves reliability in CI.

5. Added bash -i based integration test:
   - Correctly sources ~/.bashrc and evaluates alias + venv activation.
   - ‘pkgmgr --help’ is now printed for debugging without failing tests.

6. Updated unit tests across all installers:
   - Removed references to manifest installer.
   - Adjusted expectations for new behaviors (makepkg, dpkg-buildpackage, rpmbuild).
   - Added capability subsystem tests.

7. Improved flake.nix packaging logic:
   - The entire project source tree is copied into the runtime closure.
   - pkgmgr wrapper now executes runpy inside the packaged directory.

Together, these changes create a predictable, layered, capability-driven installer pipeline with consistent behavior across Arch, Debian, RPM, Nix, and Python layers.

scripts/init-nix.sh

@@ -3,14 +3,14 @@ set -euo pipefail
 
 echo ">>> Initializing Nix environment for package-manager..."
 
-# 1. /nix Store
+# 1. /nix store
 if [ ! -d /nix ]; then
   echo ">>> Creating /nix store directory"
   mkdir -m 0755 /nix
   chown root:root /nix
 fi
 
-# 2. nix-daemon aktivieren, falls vorhanden
+# 2. Enable nix-daemon if available
 if command -v systemctl >/dev/null 2>&1 && systemctl list-unit-files | grep -q nix-daemon.service; then
   echo ">>> Enabling nix-daemon.service"
   systemctl enable --now nix-daemon.service 2>/dev/null || true
@@ -18,16 +18,13 @@ else
   echo ">>> Warning: nix-daemon.service not found or systemctl not available."
 fi
 
-# 3. Gruppe nix-users sicherstellen
+# 3. Ensure nix-users group
 if ! getent group nix-users >/dev/null 2>&1; then
   echo ">>> Creating nix-users group"
-  # Debian/RPM/Arch haben alle groupadd
   groupadd -r nix-users 2>/dev/null || true
 fi
 
-# 4. Benutzer zu nix-users hinzufügen (Best-Effort)
-
-# a) Wenn loginctl vorhanden ist → alle eingeloggten User
+# 4. Add users to nix-users (best-effort)
 if command -v loginctl >/dev/null 2>&1; then
   for user in $(loginctl list-users | awk 'NR>1 {print $2}'); do
     if id "$user" >/dev/null 2>&1; then
@@ -35,7 +32,6 @@ if command -v loginctl >/dev/null 2>&1; then
       usermod -aG nix-users "$user" 2>/dev/null || true
     fi
   done
-# b) Fallback: logname (typisch bei Debian)
 elif command -v logname >/dev/null 2>&1; then
   USERNAME="$(logname 2>/dev/null || true)"
   if [ -n "$USERNAME" ] && id "$USERNAME" >/dev/null 2>&1; then
@@ -44,5 +40,5 @@ elif command -v logname >/dev/null 2>&1; then
   fi
 fi
 
-echo ">>> Nix initialization for package-manager complete."
+echo ">>> Nix initialization complete."
 echo ">>> You may need to log out and log back in to activate group membership."

scripts/pkgmgr-wrapper.sh

@@ -1,10 +1,10 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
-# Enable flakes if not already configured.
 if [[ -z "${NIX_CONFIG:-}" ]]; then
   export NIX_CONFIG="experimental-features = nix-command flakes"
 fi
 
-# Run Kevin’s package manager via Nix flake
-exec nix run "github:kevinveenbirkenbach/package-manager#pkgmgr" -- "$@"
+FLAKE_DIR="/usr/lib/package-manager"
+
+exec nix run "${FLAKE_DIR}#pkgmgr" -- "$@"