feat(infra): add self-hosted GitHub Actions runner setup

Bash setup script for Debian/Ubuntu, Dockerfile for containerized
runners, and comprehensive documentation. Installs .NET SDK, PowerShell,
Terraform, and configures the GitHub Actions runner as a systemd service
with proxmox/integration labels.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/infrastructure/runner/entrypoint.sh

@@ -0,0 +1,79 @@
+#!/usr/bin/env bash
+# =============================================================================
+# entrypoint.sh
+# Docker entrypoint for the self-hosted GitHub Actions runner.
+#
+# Required environment variables:
+#   REPO_URL      - Full GitHub repository URL (e.g. https://github.com/GoodOlClint/PSProxmoxVE)
+#   RUNNER_TOKEN  - Registration token from GitHub Settings > Actions > Runners
+#
+# Optional environment variables:
+#   RUNNER_LABELS - Comma-separated labels (default: self-hosted,proxmox,integration)
+#   RUNNER_NAME   - Runner name (default: hostname)
+#   RUNNER_GROUP  - Runner group (default: Default)
+#   EPHEMERAL     - Set to "true" for single-job ephemeral mode (default: false)
+# =============================================================================
+set -euo pipefail
+
+RUNNER_LABELS="${RUNNER_LABELS:-self-hosted,proxmox,integration}"
+RUNNER_NAME="${RUNNER_NAME:-$(hostname)}"
+RUNNER_GROUP="${RUNNER_GROUP:-Default}"
+EPHEMERAL="${EPHEMERAL:-false}"
+
+# ---------------------------------------------------------------------------
+# Validate required environment variables
+# ---------------------------------------------------------------------------
+if [[ -z "${REPO_URL:-}" ]]; then
+    echo "ERROR: REPO_URL environment variable is required."
+    echo "  Example: -e REPO_URL=https://github.com/GoodOlClint/PSProxmoxVE"
+    exit 1
+fi
+
+if [[ -z "${RUNNER_TOKEN:-}" ]]; then
+    echo "ERROR: RUNNER_TOKEN environment variable is required."
+    echo "  Get one from: ${REPO_URL}/settings/actions/runners/new"
+    exit 1
+fi
+
+# ---------------------------------------------------------------------------
+# Configure the runner
+# ---------------------------------------------------------------------------
+CONFIG_ARGS=(
+    --url "$REPO_URL"
+    --token "$RUNNER_TOKEN"
+    --labels "$RUNNER_LABELS"
+    --name "$RUNNER_NAME"
+    --runnergroup "$RUNNER_GROUP"
+    --work _work
+    --unattended
+    --replace
+)
+
+if [[ "$EPHEMERAL" == "true" ]]; then
+    CONFIG_ARGS+=(--ephemeral)
+    echo "Ephemeral mode enabled -- runner will exit after one job."
+fi
+
+echo "Configuring runner..."
+echo "  Repository: $REPO_URL"
+echo "  Name:       $RUNNER_NAME"
+echo "  Labels:     $RUNNER_LABELS"
+
+/opt/github-runner/config.sh "${CONFIG_ARGS[@]}"
+
+# ---------------------------------------------------------------------------
+# Deregister on shutdown (best-effort)
+# ---------------------------------------------------------------------------
+cleanup() {
+    echo ""
+    echo "Caught signal -- removing runner registration..."
+    /opt/github-runner/config.sh remove --token "$RUNNER_TOKEN" || true
+}
+trap cleanup SIGTERM SIGINT
+
+# ---------------------------------------------------------------------------
+# Start the runner
+# ---------------------------------------------------------------------------
+echo "Starting runner..."
+/opt/github-runner/run.sh &
+wait $!