Fix Windows OpenSSH stderr capture in app and tests

Windows OpenSSH 9.5 blocks while writing captured stderr to a pipe, even with stdin disconnected and a connection timeout. Capture stderr in a temporary file for one-shot OpenSSH calls on Windows, preserving subprocess output, text, check, and timeout behavior. Leave POSIX capture unchanged.

Use the shared runner for SSH, scp, key lookup, and streamed app-data transfers. Bound the real ssh-keygen hashing tests and keep their assertions; move the transfer-error mock to the runner seam. Add ten regression tests.

Verified the full suite on Windows 11 with bundled Python 3.12.14: 628 tests, OK (110 existing skips), 42.685s. Verified macOS Python 3.9.6: 628 tests, OK, 67.934s. Independent Codex gpt-6-sol high-reasoning review found no actionable issues. Protected RDP code is unchanged.

Co-Authored-By: GPT-6.1 Sol (Codex) <noreply@openai.com>

ui/frame_android_data.py

@@ -11,13 +11,14 @@ import tempfile
 import uuid
 
 import frame_android as android
+import frame_host
 
 REMOTE = Path(android.ROOT) / 'frame/android/app-data.py'
 
 
 def _stream(command, src=None, dst=None):
     try:
-        result = subprocess.run(['ssh', *android.SSH_OPTS, android.FRAME, command],
+        result = frame_host.run_ssh(['ssh', *android.SSH_OPTS, android.FRAME, command],
                                 stdin=src if src else subprocess.DEVNULL,
                                 stdout=dst if dst else subprocess.PIPE,
                                 stderr=subprocess.PIPE, timeout=1800)