Update binary launcher help and args for OpenAI (#148)

[bhf]

Closes #148

Description

Updated the st-k8s binary launcher to support OpenAI chat provider configuration. This includes:

• Added --openai, --openai-key, and --openai-url command-line flags.
• Updated --help output with a new "LLM Providers" section.
• Ensured environment variables and CLI flags are correctly passed to the Next.js process.

Verification

Ran ./bin/st-k8s --help to verify the output:

LLM Providers:
  --openai                       Use OpenAI as the chat provider (default: copilot)
  --openai-key <key>             Specify the OpenAI API key
  --openai-url <url>             Specify the OpenAI API base URL (default: https://api.openai.com/v1)

  Note: You can also use environment variables:
  CHAT_PROVIDER=openai
  OPENAI_API_KEY=sk-...
  OPENAI_API_URL=https://api.openai.com/v1