feat: IPv6 support and multi-IP per node (closes #60)

- maskIp handles IPv6 addresses (masks second and last group)
- maskIp handles comma-separated IP strings (masks each address)
- Add splitIps() helper to parse comma-separated IP field
- Add primaryIp() helper used by status checker (first IP wins)
- BaseNode renders each IP on its own line when comma-separated
- NodeModal placeholder shows comma-separated example
- Backend status_checker uses only first IP for connectivity checks
- Expand maskIp test suite: IPv6, comma-separated, splitIps, primaryIp

frontend/src/utils/maskIp.ts

@@ -1,12 +1,47 @@
 /**
- * Mask the last two octets of an IPv4 address.
- * e.g. "192.168.1.115" → "192.168.XX.XX"
- * Non-IPv4 strings are returned unchanged.
+ * Mask a single IP address:
+ * - IPv4 "192.168.1.115" → "192.168.XX.XX"
+ * - IPv6 "2001:db8::1"   → "2001:XX::XX"
+ * - Other strings returned unchanged.
+ */
+function maskSingle(ip: string): string {
+  const trimmed = ip.trim()
+  if (/^[\da-fA-F:]+$/.test(trimmed) && trimmed.includes(':')) {
+    const groups = trimmed.split(':')
+    if (groups.length >= 2) {
+      groups[1] = 'XX'
+      groups[groups.length - 1] = 'XX'
+      return groups.join(':')
+    }
+  }
+  const parts = trimmed.split('.')
+  if (parts.length === 4) return `${parts[0]}.${parts[1]}.XX.XX`
+  return trimmed
+}
+
+/**
+ * Mask all IPs in a comma-separated string.
+ * e.g. "192.168.1.1, 2001:db8::1" → "192.168.XX.XX, 2001:XX::XX"
  */
 export function maskIp(ip: string): string {
-  const parts = ip.split('.')
-  if (parts.length === 4) return `${parts[0]}.${parts[1]}.XX.XX`
-  return ip
+  if (!ip) return ip
+  return ip.split(',').map(maskSingle).join(', ')
+}
+
+/**
+ * Split a comma-separated IP string into an array of trimmed values.
+ * Empty string returns [].
+ */
+export function splitIps(ip: string): string[] {
+  if (!ip?.trim()) return []
+  return ip.split(',').map((s) => s.trim()).filter(Boolean)
+}
+
+/**
+ * Return the first IP from a comma-separated string (used for status checks).
+ */
+export function primaryIp(ip: string): string {
+  return splitIps(ip)[0] ?? ''
 }
 
 export function primaryIp(ip: string): string {