fix(status): use ms timeout for ping on macOS

ping(8) -W flag is milliseconds on macOS, seconds on Linux. Code used
-W 1 for both, giving macOS a 1ms timeout that fails any host with
RTT >1ms (typical wifi/mesh is 2-10ms).

Use -W 1000 on darwin to match the intended 1s timeout. Add regression
test asserting the platform-specific value.

backend/app/services/status_checker.py

@@ -60,8 +60,14 @@ async def check_node(check_method: str, target: str | None, ip: str | None) -> d
 
 
 async def _ping(host: str) -> bool:
+    # ping(8) -W flag units differ by OS:
+    #   Linux:   seconds        (-W 1   = 1s)
+    #   macOS:   milliseconds   (-W 1   = 1ms — fails for any RTT >1ms)
+    #   Windows: -w in ms       (-w 1000 = 1s)
     if sys.platform == "win32":
         args = ["ping", "-n", "1", "-w", "1000", host]
+    elif sys.platform == "darwin":
+        args = ["ping", "-c", "1", "-W", "1000", host]
     else:
         args = ["ping", "-c", "1", "-W", "1", host]
     proc = await asyncio.create_subprocess_exec(