Document .continue/configs/ directory for local config profiles

[continue]

Summary

PR #11935 added support for .continue/configs/ as a third directory (alongside .continue/agents/ and .continue/assistants/) for loading local config profiles.

What needs to be documented

1. Feature overview: YAML files placed in .continue/configs/ (workspace or global) are now discovered, watched, and loaded as local profiles
2. Location options: Both ~/.continue/configs/ (global) and workspace-level .continue/configs/ are supported
3. Update the config documentation: The docs/guides/understanding-configs.mdx and docs/reference.mdx pages should mention this directory alongside the existing directory documentation
4. Relationship with other directories: Explain how this relates to .continue/agents/ and .continue/assistants/

Related PR

#11935

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Co-Authored-By: Continue noreply@continue.dev