feat: Implement machine_id based host identification

- Add machine_id field to hosts schema (unique, indexed)
- Remove unique constraint from friendly_name (allow duplicate hostnames)
- Agent installer now generates/reads persistent machine_id
- Proxmox script retrieves machine_id from LXC containers
- Backend will check machine_id instead of hostname for duplicates

This allows multiple hosts with same hostname to coexist in PatchMon

agents/patchmon_install.sh

@@ -109,14 +109,32 @@ cleanup_old_files() {
 # Run cleanup at start
 cleanup_old_files
 
+# Generate or retrieve machine ID
+get_machine_id() {
+    # Try multiple sources for machine ID
+    if [[ -f /etc/machine-id ]]; then
+        cat /etc/machine-id
+    elif [[ -f /var/lib/dbus/machine-id ]]; then
+        cat /var/lib/dbus/machine-id
+    else
+        # Fallback: generate from hardware info (less ideal but works)
+        echo "patchmon-$(cat /sys/class/dmi/id/product_uuid 2>/dev/null || cat /proc/sys/kernel/random/uuid)"
+    fi
+}
+
 # Parse arguments from environment (passed via HTTP headers)
 if [[ -z "$PATCHMON_URL" ]] || [[ -z "$API_ID" ]] || [[ -z "$API_KEY" ]]; then
     error "Missing required parameters. This script should be called via the PatchMon web interface."
 fi
 
+# Get unique machine ID for this host
+MACHINE_ID=$(get_machine_id)
+export MACHINE_ID
+
 info "🚀 Starting PatchMon Agent Installation..."
 info "📋 Server: $PATCHMON_URL"
 info "🔑 API ID: ${API_ID:0:16}..."
+info "🆔 Machine ID: ${MACHINE_ID:0:16}..."
 
 # Display diagnostic information
 echo ""
@@ -261,6 +279,33 @@ if [[ -f "/var/log/patchmon-agent.log" ]]; then
 fi
 
 # Step 4: Test the configuration
+# Check if this machine is already enrolled
+info "🔍 Checking if machine is already enrolled..."
+existing_check=$(curl $CURL_FLAGS -s -X POST \
+    -H "X-API-ID: $API_ID" \
+    -H "X-API-KEY: $API_KEY" \
+    -H "Content-Type: application/json" \
+    -d "{\"machine_id\": \"$MACHINE_ID\"}" \
+    "$PATCHMON_URL/api/v1/hosts/check-machine-id" \
+    -w "\n%{http_code}" 2>&1)
+
+http_code=$(echo "$existing_check" | tail -n 1)
+response_body=$(echo "$existing_check" | sed '$d')
+
+if [[ "$http_code" == "200" ]]; then
+    already_enrolled=$(echo "$response_body" | jq -r '.exists' 2>/dev/null || echo "false")
+    if [[ "$already_enrolled" == "true" ]]; then
+        warning "⚠️  This machine is already enrolled in PatchMon"
+        info "Machine ID: $MACHINE_ID"
+        info "Existing host: $(echo "$response_body" | jq -r '.host.friendly_name' 2>/dev/null)"
+        info ""
+        info "The agent will be reinstalled/updated with existing credentials."
+        echo ""
+    else
+        success "✅ Machine not yet enrolled - proceeding with installation"
+    fi
+fi
+
 info "🧪 Testing API credentials and connectivity..."
 if /usr/local/bin/patchmon-agent.sh test; then
     success "✅ TEST: API credentials are valid and server is reachable"