Fix Windows hangs found against a real Frame

- Child processes never inherit the server's stdin. Under the app it's the pipe
  held open for --exit-on-eof, and Windows' ssh.exe waited on it forever, so
  captures, the screenshot list and Android apps timed out.
- frame_connect's key check accepts a first-seen host key (as the copy step
  does), so an already-authorized key doesn't trigger a password prompt.

Verified on Windows 11, Ubuntu and macOS against a Steam Frame: status,
headset and desktop captures, live video, library, Android apps, screenshots
and upload.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

ui/frame_host.py

@@ -185,7 +185,7 @@ def clipboard_text():
     for cmd in cmds:
         if not shutil.which(cmd[0]):
             continue
-        r = subprocess.run(cmd, capture_output=True, timeout=10)
+        r = subprocess.run(cmd, capture_output=True, stdin=subprocess.DEVNULL, timeout=10)
         if r.returncode == 0:
             text = r.stdout.decode("utf-8", errors="replace")
             return text[:-2] if WINDOWS and text.endswith("\r\n") else text
@@ -197,7 +197,7 @@ def clipboard_text():
 def ssh_hostname(alias):
     """The real host name an ssh alias points at (`ssh -G`), for non-SSH clients like RDP."""
     try:
-        out = subprocess.run(["ssh", "-G", alias], capture_output=True, text=True, timeout=10).stdout
+        out = subprocess.run(["ssh", "-G", alias], capture_output=True, stdin=subprocess.DEVNULL, text=True, timeout=10).stdout
     except (OSError, subprocess.TimeoutExpired):
         return alias
     for line in out.splitlines():