[Security] NVIDIA API key exposed in process list when creating inference provider

[ericksoa]

During onboarding, openshell provider create is called with the API key interpolated directly into the shell command:

openshell provider create --name nvidia-nim --type openai \
  --credential "NVIDIA_API_KEY=${process.env.NVIDIA_API_KEY}" ...

While this command is running, any user on the machine can see the full API key via ps aux. On shared systems (e.g., DGX Spark), this is a real credential exposure risk.

Expected: Pass the credential via stdin, environment variable, or a temporary file with restricted permissions — not as a command-line argument.

Related PRs that partially address this:

• security: replace shell string interpolation with argv arrays #148 — replace shell string interpolation with argv arrays
• fix(orchestrator): use provider-specific credential environment variable #191 — use provider-specific credential environment variable