Windows: fix ssh config ACL, link-local IPv6, and setup under python -I

- ~/.ssh/config writes swapped in a temp file that inherited the .ssh folder's
  ACL; Windows' OpenSSH refuses one granting another account (even a deleted
  one) more than read: "Bad owner or permissions". Writes now give the file an
  owner-only ACL (frame_host.make_private), and the server repairs a refused
  config once per run and retries.
- frame_link.probe named a link-local IPv6 zone with if_indextoname, which on
  Windows is "ethernet_32769"; Windows' ssh can't resolve that, so a headset
  found at fe80:: showed as "can't find the Frame". Use the zone number there.
- frame_connect.py imports frame_host (since #60), but the app runs it with
  python -I, which leaves its folder off sys.path: Set Up Connection exited
  with ModuleNotFoundError. Add the folder, as server.py does.

Verified on a Windows 11 VM against OpenSSH_for_Windows 9.5p2: the old write
reproduces the reported error with an orphan SID's Modify ACE; the new write,
repair and server retry all leave a config ssh accepts; ssh to %ethernet_32769
fails to resolve while %5 connects.

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

ui/frame_link.py

@@ -108,7 +108,8 @@ def probe(host, port, timeout=PROBE_TIMEOUT, update=None):
         ip = addr[0]
         if family == socket.AF_INET6 and len(addr) > 3 and addr[3] and "%" not in ip:
             try:  # a link-local IPv6 address only works with its interface
-                ip = f"{ip}%{socket.if_indextoname(addr[3])}"
+                # Windows' ssh takes only the number: its names ("wireless_32768") don't resolve.
+                ip = f"{ip}%{addr[3] if frame_host.WINDOWS else socket.if_indextoname(addr[3])}"
             except (OSError, AttributeError):
                 pass
         left = deadline - now()