feat(deployment): replace monster scripts with modular helper scripts (#87)

- Add install.sh orchestrator with upgrade support
- Add 6 helper scripts (<100 lines each) replacing 700-800 line monsters
- Add deployment/linux/furt.service systemd template
- Support both fresh install and upgrade modes
- Platform-aware detection (OpenBSD/FreeBSD vs Linux)
- Skip user/service creation in upgrade mode
- Preserve existing configuration during updates
- Remove merkwerk dependency from production install script

Helper scripts:
- scripts/setup-user.sh - Create system user (_furt/furt)
- scripts/setup-directories.sh - Create directory structure
- scripts/sync-files.sh - Copy source files to installation
- scripts/create-service.sh - Create system service from templates
- scripts/validate-config.sh - Validate furt.conf syntax
- scripts/health-check.sh - Basic health check functionality

Closes DAW/furt#87

scripts/create-service.sh

@@ -0,0 +1,41 @@
+#!/bin/sh
+# scripts/create-service.sh - Create system service for furt using repository templates
+
+set -e
+
+# Check if we're in furt source directory
+if [ ! -d "deployment" ]; then
+    echo "Error: deployment/ directory not found - not in furt source directory?"
+    exit 1
+fi
+
+if [ "$(uname)" = "OpenBSD" ]; then
+    # Use OpenBSD rc.d template from repository
+    if [ ! -f "deployment/openbsd/rc.d-furt" ]; then
+        echo "Error: deployment/openbsd/rc.d-furt template not found"
+        exit 1
+    fi
+    
+    cp deployment/openbsd/rc.d-furt /etc/rc.d/furt
+    chmod +x /etc/rc.d/furt
+    echo "furt_flags=" >> /etc/rc.conf.local
+    rcctl enable furt
+    echo "OpenBSD service created and enabled using repository template"
+    
+elif [ "$(uname)" = "Linux" ]; then
+    # Use systemd template from repository
+    if [ ! -f "deployment/linux/furt.service" ]; then
+        echo "Error: deployment/linux/furt.service template not found"
+        exit 1
+    fi
+    
+    cp deployment/linux/furt.service /etc/systemd/system/
+    systemctl daemon-reload
+    systemctl enable furt
+    echo "Linux systemd service created and enabled using repository template"
+    
+else
+    echo "Unsupported operating system for service creation"
+    exit 1
+fi
+