Add release workflow, install.sh and update.sh for customer deployment

- release.yml: triggered by git tag v*, builds assets, creates ZIP,
  attaches to Gitea release
- install.sh: interactive first-time setup (DB config, key:generate,
  migrate, seed, cache)
- update.sh: update existing installation (clear caches, migrate, rebuild)

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

update.sh

@@ -0,0 +1,51 @@
+#!/bin/bash
+# WITshop Update
+# Ausführen mit: bash update.sh
+
+set -e
+GREEN='\033[0;32m'; YELLOW='\033[1;33m'; NC='\033[0m'
+
+echo ""
+echo "=================================="
+echo "  WITshop Update"
+echo "=================================="
+echo ""
+
+PHP=$(which php 2>/dev/null || echo "/opt/plesk/php/8.4/bin/php")
+COMPOSER=$(which composer 2>/dev/null || echo "/usr/local/psa/var/modules/composer/composer.phar")
+
+if [ ! -f ".env" ]; then
+  echo "FEHLER: Keine .env gefunden. Bitte zuerst install.sh ausführen."
+  exit 1
+fi
+
+echo "--- Cache leeren ---"
+$PHP -d open_basedir="" artisan config:clear
+$PHP -d open_basedir="" artisan route:clear
+$PHP -d open_basedir="" artisan view:clear
+$PHP -d open_basedir="" artisan cache:clear
+echo -e "${GREEN}✓ Cache geleert${NC}"
+
+echo ""
+echo "--- Abhängigkeiten aktualisieren ---"
+$PHP -d open_basedir="" $COMPOSER install --no-dev --optimize-autoloader --no-interaction
+echo -e "${GREEN}✓ Composer${NC}"
+
+echo ""
+echo "--- Migrationen ausführen ---"
+$PHP -d open_basedir="" artisan migrate --force
+$PHP -d open_basedir="" artisan db:seed --class=EmailTemplateSeeder --force
+echo -e "${GREEN}✓ Datenbank aktualisiert${NC}"
+
+echo ""
+echo "--- Cache aufbauen ---"
+$PHP -d open_basedir="" artisan config:cache
+$PHP -d open_basedir="" artisan route:cache
+$PHP -d open_basedir="" artisan view:cache
+echo -e "${GREEN}✓ Cache erstellt${NC}"
+
+echo ""
+echo "=================================="
+echo -e "${GREEN}  Update abgeschlossen!${NC}"
+echo "=================================="
+echo ""