fix: pass allow_unicode=True in save_vault_yaml

Matches the pattern already used in infra's scripts/utils/secrets.py:save_yaml.
Prevents corruption of non-ASCII content in vault files.

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

src/devx/utils/vault.py

@@ -102,7 +102,7 @@ def save_vault_yaml(path: Path, data: dict, vault_pass: Path | None = None) -> N
         data: Data to serialize.
         vault_pass: Path to the vault-password file (optional).
     """
-    plain = yaml.dump(data, default_flow_style=False, sort_keys=False)
+    plain = yaml.dump(data, default_flow_style=False, sort_keys=False, allow_unicode=True)
     with open(path, "w", encoding="utf-8") as f:
         f.write(plain)
     if vault_pass is not None and vault_pass.exists():