fix(cookbook): set UTF-8 encoding for detached download/serve subprocesses (#1599)

On Windows, Python defaults to the active code page (cp1252) for
subprocess I/O. HuggingFace CLI outputs U+2713 (✓) when validating
tokens, which cp1252 cannot encode, crashing the download process.

Set PYTHONUTF8=1 and PYTHONIOENCODING=utf-8 in the subprocess
environment so Unicode output from hf/pip/llama-server is handled
correctly.

Fixes #1543

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

routes/cookbook_routes.py

@@ -383,11 +383,15 @@ def setup_cookbook_routes() -> APIRouter:
                 encoding="utf-8",
             )
             argv = [os.environ.get("ComSpec", "cmd.exe"), "/c", str(script_path)]
+        env = os.environ.copy()
+        env["PYTHONUTF8"] = "1"
+        env["PYTHONIOENCODING"] = "utf-8"
         proc = subprocess.Popen(
             argv,
             stdout=subprocess.DEVNULL,
             stderr=subprocess.DEVNULL,
             stdin=subprocess.DEVNULL,
+            env=env,
             **detached_popen_kwargs(),
         )
         pid_path.write_text(str(proc.pid), encoding="utf-8")