Refine setup workflows and add architecture map

- Split virgin tests into separate root and user GitHub Actions workflows
  (test-virgin-root, test-virgin-user) and adjust Arch container flows
- Introduce scripts/installation/venv-create.sh and reuse it from
  scripts/installation/main.sh with separate root/system and user/dev paths
- Add PKGMGR architecture & setup map (assets/map.png) and section in README
  with link to the up-to-date master page
- Simplify README by removing outdated Docker quickstart, usage examples,
  and AI footer
- Extend .gitignore to exclude src/source artifacts

https://chatgpt.com/share/6939bbfe-5cb0-800f-8ea8-95628dc911f5

.github/workflows/test-virgin-root.yml

@@ -0,0 +1,64 @@
+name: Test Virgin Root
+
+on:
+  push:
+    branches:
+      - main
+      - master
+      - develop
+      - "*"
+  pull_request:
+
+jobs:
+  test-virgin-root:
+    runs-on: ubuntu-latest
+    timeout-minutes: 45
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Show Docker version
+        run: docker version
+
+      - name: Virgin Arch pkgmgr flake test (root)
+        run: |
+          set -euo pipefail
+
+          echo ">>> Starting virgin ArchLinux container test (root, with shared caches)..."
+
+          docker run --rm \
+            -v "$PWD":/src \
+            -v pkgmgr_repos:/root/Repositories \
+            -v pkgmgr_pip_cache:/root/.cache/pip \
+            -w /src \
+            archlinux:latest \
+            bash -lc '
+              set -euo pipefail
+
+              echo ">>> Updating and upgrading Arch system..."
+              pacman -Syu --noconfirm git python python-pip nix >/dev/null
+
+              echo ">>> Creating isolated virtual environment for pkgmgr..."
+              python -m venv /tmp/pkgmgr-venv
+
+              echo ">>> Activating virtual environment..."
+              source /tmp/pkgmgr-venv/bin/activate
+
+              echo ">>> Upgrading pip (cached)..."
+              python -m pip install --upgrade pip >/dev/null
+
+              echo ">>> Installing pkgmgr from current source tree (cached pip)..."
+              python -m pip install /src >/dev/null
+
+              echo ">>> Enabling Nix experimental features..."
+              export NIX_CONFIG="experimental-features = nix-command flakes"
+
+              echo ">>> Running: pkgmgr update pkgmgr --clone-mode shallow --no-verification"
+              pkgmgr update pkgmgr --clone-mode shallow --no-verification
+
+              echo ">>> Running: pkgmgr version pkgmgr"
+              pkgmgr version pkgmgr
+
+              echo ">>> Virgin Arch (root) test completed successfully."
+            '