fix(integration): restore subprocess encoding/stdin guards dropped in simplification

Simplification workers collapsed subprocess call sites into shared kwargs
helpers and dropped the Windows/TUI safety kwargs on the way:

- encoding='utf-8', errors='replace' restored on text=True runs in
  copilot_acp_client, hermes_cli/setup (vercel install), managed_uv
  (codesign steps), local_runtime/hardware._stdout, a2a adapter.
- stdin=subprocess.DEVNULL restored on copilot probe, verify/runner
  _SUBPROCESS_KW, iron_proxy._run, google_meet playwright/system_profiler,
  simplex convert, whatsapp _RUN_TEXT, mem0 ollama serve Popen.
  google_meet sudo/brew install keeps inherited stdin (user-confirmed,
  may prompt) — marked noqa: subprocess-stdin.
- Windows-safe SIGKILL: getattr(signal, 'SIGKILL', SIGTERM) in
  verify/runner; photon _kill call re-marked windows-footgun: ok
  (unreachable on win32).
- scripts/check_subprocess_stdin.py now recognizes **kwargs splats
  (**_KW / **_kw(...)) ONLY when the same-file definition provably sets
  stdin= — covers tui_gateway _capture_run_kwargs/run_kw. Parity test added.

plugins/platforms/simplex/adapter.py

@@ -725,7 +725,7 @@ class SimplexAdapter(BasePlatformAdapter):
                 if needs_png:
                     png_path = str(p.with_suffix(".png"))
                     subprocess.run(["convert", file_path, png_path],
-                                   check=True, capture_output=True, timeout=30)
+                                   check=True, capture_output=True, timeout=30, stdin=subprocess.DEVNULL)
                 with tempfile.NamedTemporaryFile(suffix=".jpg", delete=False) as tmp:
                     tmp_path = tmp.name
                 subprocess.run(