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

backend/app/services/status_checker.py

@@ -19,7 +19,9 @@ async def check_node(check_method: str, target: str | None, ip: str | None) -> d
     if check_method == "none":
         return {"status": "online", "response_time_ms": None}
 
-    host = target or ip
+    # Use only the first IP when the field contains comma-separated addresses
+    raw_ip = ip.split(",")[0].strip() if ip else None
+    host = target or raw_ip
     if not host:
         return {"status": "unknown", "response_time_ms": None}