fix(code-group): add TOML language preset to fix missing icon

[20syldev]

Summary

Fixes mintlify/mdx#40.

<CodeGroup dropdown> with a TOML code block was showing a YAML icon instead of a TOML icon. The root cause was that SNIPPET_PRESETS had no entry for toml, so getIconKey("toml") returned undefined, causing the icon lookup to fall back to the YAML devicon.

• Added a toml preset with displayName: "TOML" and shikiLanguage: "yaml" (consistent with the existing SHIKI_LANG_MAP which uses YAML grammar for TOML highlighting)
• Made httpSnippet optional in SnippetPreset since config/data formats like TOML don't have an HTTP snippet target

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Note

Low Risk
Low risk: small config/type change that only affects language preset lookup and optional handling of httpSnippet for non-HTTP formats.

Overview
Fixes missing TOML language handling in code-group/snippet preset resolution by adding a toml entry (with displayName: "TOML" and YAML-based Shiki highlighting) so icon lookup can return a TOML devicon instead of falling back.

Updates the SnippetPreset type to make httpSnippet optional, allowing data/config formats like TOML to exist without an HTTP snippet generation target.

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