Add offline dependency download scripts for air-gapped environment

- download-all-dependencies.sh: Downloads Qt6 6.10.2, source tarballs, and Ubuntu .deb packages
- download-deb-packages.sh: Downloads Ubuntu .deb packages in Docker container
- verify-offline-cache.sh: Verifies offline cache completeness
- offline-cache/README.md: Documentation for offline cache structure and usage
- .gitignore: Exclude external-dependencies/offline-cache/ from version control (2.3GB)

The offline cache must be transferred to air-gapped environment via secure media.
Excluded from git due to size and security best practices.

Co-authored-by: Copilot <2235566219+Copilot@users.noreply.github.com>
Entire-Checkpoint: 01M6PFZM0GHMBF46BKYPKZC192

external-dependencies/scripts/download-all-dependencies.sh

@@ -0,0 +1,118 @@
+#!/bin/bash
+#
+# Download all external dependencies for air-gapped environment
+# Creates offline package cache for Jenkins/Dockerfile use
+#
+# Usage: ./download-all-dependencies.sh [output-directory]
+#
+# Output directory structure:
+#   offline-cache/
+#   ├── qt6/                    # Qt6 packages from aqtinstall
+#   ├── src/                    # Source tarballs (KDReports, Log4Qt, Grantlee)
+#   ├── deb/                    # Ubuntu .deb packages
+#   └── scripts/                # Installation scripts for offline use
+#
+
+set -euo pipefail
+
+# Configuration
+OUTPUT_DIR="${1:-./offline-cache}"
+QT_VERSION="6.10.2"
+QT_MODULES="qtmultimedia qtserialport qtimageformats qtwebsockets qtwebengine qtpdf qtwebview qt5compat qtwebchannel qtpositioning qtlocation qtsensors"
+
+# Air-gapped environment configuration (from Dockerfiles)
+NEXUS_REPO="http://remote-repo.sl.defence-elec.de:8081"
+PIP_INDEX_URL="${NEXUS_REPO}/repository/proxypipy/"
+APT_SOURCES="${NEXUS_REPO}/repository/ubuntu"
+
+echo "========================================="
+echo "Downloading External Dependencies"
+echo "========================================="
+echo "Output directory: ${OUTPUT_DIR}"
+echo "Qt Version: ${QT_VERSION}"
+echo "========================================="
+
+# Create directory structure
+mkdir -p "${OUTPUT_DIR}"/{qt6,src,deb,scripts}
+
+# Run download in Docker container with proper environment
+echo ""
+echo "Running download in Ubuntu 26.04 Docker container..."
+echo ""
+
+docker run --rm \
+    -v "$(pwd)/${OUTPUT_DIR}:/cache" \
+    -e PIP_INDEX_URL="${PIP_INDEX_URL}" \
+    -e NEXUS_REPO="${NEXUS_REPO}" \
+    ubuntu:26.04 \
+    bash -c "
+set -euo pipefail
+
+OUTPUT_DIR='/cache'
+QT_VERSION='${QT_VERSION}'
+QT_MODULES='${QT_MODULES}'
+NEXUS_REPO='${NEXUS_REPO}'
+PIP_INDEX_URL='${PIP_INDEX_URL}'
+
+echo '=== Installing required packages ==='
+apt-get update -qq
+apt-get install -y -qq python3 python3-venv python3-pip git wget curl apt-transport-https
+
+echo ''
+echo '=== Setting up Python virtual environment for aqtinstall ==='
+python3 -m venv /tmp/aqtinstall_venv
+source /tmp/aqtinstall_venv/bin/activate
+
+# Install aqtinstall from standard PyPI (not available in internal proxy)
+echo 'Installing aqtinstall from standard PyPI...'
+pip install --quiet --index-url https://pypi.org/simple aqtinstall
+
+echo ''
+echo '=== Downloading Qt6 \${QT_VERSION} ==='
+aqt install-qt linux desktop \${QT_VERSION} linux_gcc_64 \\
+    --modules \${QT_MODULES} \\
+    --outputdir /cache/qt6 \\
+    --base \${NEXUS_REPO}/repository/qt-mirror/
+
+echo ''
+echo 'Qt6 downloaded to /cache/qt6'
+
+echo ''
+echo '=== Downloading Source Tarballs ==='
+
+# KDReports
+echo 'Downloading KDReports 2.3.0...'
+git clone --depth 1 --branch kdreports-2.3.0 \\
+    https://github.com/KDAB/KDReports.git \\
+    /tmp/KDReports
+tar -czf /cache/src/KDReports-2.3.0.tar.gz -C /tmp KDReports
+rm -rf /tmp/KDReports
+
+# Log4Qt
+echo 'Downloading Log4Qt 2.0.0...'
+git clone --depth 1 --branch v2.0.0 \\
+    https://github.com/MEONMedical/Log4Qt.git \\
+    /tmp/Log4Qt
+tar -czf /cache/src/Log4Qt-2.0.0.tar.gz -C /tmp Log4Qt
+rm -rf /tmp/Log4Qt
+
+# Grantlee
+echo 'Downloading Grantlee (master branch)...'
+git clone --depth 1 \\
+    https://github.com/steveire/grantlee.git \\
+    /tmp/grantlee
+GRANTLEE_COMMIT=\$(cd /tmp/grantlee && git rev-parse HEAD)
+echo 'Grantlee commit: \${GRANTLEE_COMMIT}'
+tar -czf /cache/src/grantlee-\${GRANTLEE_COMMIT:0:7}.tar.gz -C /tmp grantlee
+rm -rf /tmp/grantlee
+
+echo ''
+echo 'Source tarballs downloaded to /cache/src'
+
+# Cleanup
+deactivate 2>/dev/null || true
+rm -rf /tmp/aqtinstall_venv
+
+echo ''
+echo '=== Download Complete ==='
+"