The GPT 4.1 system prompt is not being used by Goose

[simonsickle]

Describe the bug

Note: Please check the common issues on https://block.github.io/goose/docs/troubleshooting before filing a report

Because of a typo in the way the markdown file is referenced, the GPT 4.1 prompt is not being loaded properly.

To Reproduce
Steps to reproduce the behavior:

1. View the file: https://github.com/block/goose/blob/main/crates/goose/src/agents/prompt_manager.rs#L51 and notice the underscore in the name
2. View the prompt, notice the dot in the name https://github.com/block/goose/blob/main/crates/goose/src/prompts/system_gpt_4.1.md?plain=1

Expected behavior
The markdown file should be properly referenced to load properly.

Please provide following information:

• OS & Arch: Any
• Interface: UI/CLI
• Version: [e.g. v1.0.2]
• Extensions enabled: [e.g. Computer Controller, Figma]
• Provider & Model: OpenAI GPT 4.1

Additional context
Add any other context about the problem here.

[michaelneale]

I think we could possibly retire custom system prompts - as the smarter models seem to need them less?