Fix review findings and Windows setup issues found in testing

- Run the server with -X utf8: the bundled Windows Python ignores PYTHON* variables.
- Quote every argument in Windows terminal commands, so cmd metacharacters are literal.
- frame_connect: accept HOST:PORT, validate input, retry the config swap while
  Windows' ssh.exe holds ~/.ssh/config locked, and don't apply 0o700 on Windows.
- Never use rsync on Windows; unbounded stream queue; validate FRAME_ALIAS;
  more Linux terminals; bundle the window icon; docs and wording fixes.

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

app/build/fetch-python.js

@@ -28,7 +28,8 @@ function get(url) {
 }
 
 (async () => {
-  if (fs.existsSync(path.join(OUT, "python.exe")) && fs.readFileSync(path.join(OUT, ".version"), "utf8") === VERSION) {
+  const stamp = path.join(OUT, ".version");
+  if (fs.existsSync(path.join(OUT, "python.exe")) && fs.existsSync(stamp) && fs.readFileSync(stamp, "utf8") === VERSION) {
     console.log(`Python ${VERSION} already in ${OUT}`);
     return;
   }