feat(prepare-win): stream toolchain/WU output to the console live

pypsrp's execute_ps is fully blocking, so Install-CIToolchain / Windows
Update output only appeared at the end behind a "still running (Ns)"
heartbeat. Add WinRmTransport.run_streaming: drive the script via pypsrp's
incremental begin_invoke/poll_invoke, emitting output, Write-Host
(information) and error stream lines as they arrive over the same WinRM
channel.

_run_with_heartbeat now prefers run_streaming (suppressing the CI_EXITCODE
marker line) and falls back to the blocking heartbeat only on an unexpected
pypsrp error — TransportError still propagates so the 3010 reboot handling
is unaffected.

src/ci_orchestrator/commands/template.py

@@ -367,12 +367,26 @@ def _run_with_heartbeat(
     check: bool = True,
     heartbeat: int = 30,
 ) -> WinRmResult:
-    """Run *script* via *transport* and print a heartbeat line every *heartbeat* s.
+    """Run *script* and show its output live; fall back to a heartbeat line.
 
-    pypsrp's execute_ps is fully blocking — no streaming.  The heartbeat
-    thread reassures the operator that the command is still running during
-    long-running steps (e.g. Windows Update, which can take 20-40 min).
+    Prefers :meth:`WinRmTransport.run_streaming` so long steps (toolchain
+    install, Windows Update — 20-40 min) print progress as it happens. The
+    ``CI_EXITCODE:`` marker line is suppressed from the live echo. If streaming
+    is unavailable/fails, fall back to the blocking run + periodic heartbeat.
     """
+    def _echo_line(line: str) -> None:
+        if not line.strip().startswith("CI_EXITCODE:"):
+            click.echo(line)
+
+    try:
+        return transport.run_streaming(script, _echo_line, check=check)
+    except TransportError:
+        # Connection/command errors must propagate — e.g. the VM rebooting
+        # mid-update is caught upstream and treated as exit 3010.
+        raise
+    except Exception as exc:  # pypsrp API quirk — degrade to the blocking path
+        click.echo(f"  [WARN] live streaming failed ({exc}); using heartbeat.", err=True)
+
     result_holder: list[WinRmResult] = []
     exc_holder: list[BaseException] = []
     stop_event = threading.Event()