feat(PROJ-17): Admin Dashboard Systemauslastung immer anzeigen

- Systemauslastungs-Sektion wird immer gerendert (nicht nur bei Erfolg)
- Fehlermeldung wenn /api/admin/system/stats nicht erreichbar ist
- Feature-Status auf In Review gesetzt

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

setup.sh

@@ -0,0 +1,49 @@
+#!/usr/bin/env bash
+# setup.sh — First-time build setup for mailarchive
+# Run once on a machine with internet access.
+# After this, the project builds and tests without internet.
+set -e
+
+echo "==> Checking Go version"
+go version
+GO_MINOR=$(go version | grep -oP 'go1\.\K[0-9]+')
+if [ "$GO_MINOR" -lt 22 ]; then
+  echo "ERROR: Go 1.22+ required"
+  exit 1
+fi
+
+echo ""
+echo "==> Downloading dependencies (go mod tidy)"
+go mod tidy
+
+echo ""
+echo "==> Verifying modules"
+go mod verify
+
+echo ""
+echo "==> Building (Bleve backend — default)"
+make build
+
+echo ""
+echo "==> Binary sizes"
+ls -lh bin/
+
+echo ""
+echo "==> Running tests"
+make test
+
+echo ""
+echo "========================================"
+echo "  Build successful!"
+echo ""
+echo "  To start the daemon:"
+echo "    sudo make install"
+echo "    sudo systemctl start mailarchive"
+echo ""
+echo "  Or run directly:"
+echo "    ./bin/archivmail --config config/config.yml"
+echo ""
+echo "  To build with Xapian (optional, needs libxapian-dev):"
+echo "    apt install libxapian-dev"
+echo "    make build-xapian"
+echo "========================================"