fix: add explicit UTF-8 encoding to all subprocess text=True calls (#53428)

On Windows with Chinese locale (GBK), subprocess.run(text=True) without
explicit encoding causes UnicodeDecodeError crashes. This fix adds
encoding='utf-8', errors='replace' to all subprocess.run() and
subprocess.Popen() calls that use text=True across 76 non-test Python files.

Fixes #53428 (master tracker for Windows GBK locale crash).

Note: credential_pool.py and electron changes excluded per reviewer request —
those will be submitted as separate focused PRs.

batch_runner.py

@@ -282,7 +282,7 @@ def _process_single_prompt(
                         print(f"   Prompt {prompt_index}: Pulling docker image {container_image}...", flush=True)
                     pull = _sp.run(
                         ["docker", "pull", container_image],
-                        capture_output=True, text=True, timeout=600,
+                        capture_output=True, text=True, encoding='utf-8', errors='replace', timeout=600,
                     )
                     if pull.returncode != 0:
                         return {