[svelte-check] Use "machine" format by default if svelte-check is ran by a llm agent

[mquandalle]

Description

svelte-check is quite verbose by default, which is why --format machine exists.
But llm agents like Claude code or Openai codex don't know about this option by default.

Bun is doing something interesting when bun test is ran : https://bun.com/docs/cli/test#ai-agent-integration
It detects CLAUDECODE=1 env variable, and adapt the output format to use a more concise one

Proposed solution

Change the default format of svelte-check when a LLM agent environment is detected

Alternatives

An alternative would be to add instruction in the svelte mcp prompt, to use --format machine when calling svelte-check, but I'm not a fan of complicating prompts with a lot of details about how to call each cli tool.

Additional Information, eg. Screenshots

No response