feat(launch): support no-args listing, --config flag, and proper -- arg passthrough

[Copilot]

docker model launch required an APP argument and errored without one, had no way to inspect configuration without launching, and didn't properly separate integration args via --.

Changes

• No-args mode: docker model launch now lists supported apps with descriptions and install status instead of erroring
• --config flag: Prints environment variables and endpoint configuration for an app without launching it
• -- separator enforcement: Extra args without -- now produce a clear error; args after -- are passed through to the integration
• App descriptions: Added human-readable descriptions for all supported apps

$ docker model launch
Supported apps:

  anythingllm     RAG platform with Docker Model Runner provider
  claude          Claude Code AI assistant (not installed)
  codex           Codex CLI (not installed)
  openclaw        Open Claw AI assistant (not installed)
  opencode        Open Code AI code editor (not installed)
  openwebui       Open WebUI for models

Usage: docker model launch APP [-- APP_ARGS...]

$ docker model launch claude --config
Configuration for claude (host app):
  Environment:
    ANTHROPIC_BASE_URL=http://127.0.0.1:12434/anthropic
    ANTHROPIC_API_KEY=sk-docker-model-runner

$ docker model launch claude -- --help   # passes --help to claude

12 new tests covering listing, config output, passthrough args, and error cases. Docs updated.

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