fix: resolve duplicate #validation anchor in configuration.mdx

[Copilot]

The ### Validation heading in docs/configuration.mdx produced a #validation anchor that conflicted with the ## Validation heading in the imported _configuration_reference.mdx pulled in at build time.

Changes

• docs/configuration.mdx: renamed ### Validation → ### Basic Validation to eliminate the anchor conflict
• Removed the now-unnecessary <a id="validation-subset"></a> workaround anchor tag
• Added a link from the Basic Validation section to the full Validation section in the imported configuration reference below
• .gitignore: updated to exclude docs/_configuration_reference.mdx (the fetched reference file extension had changed from .md to .mdx, causing it to slip through the ignore rule)

[chrjohn]

@copilot well, that doesn't look too good. Build is falling...

[Copilot]

@copilot well, that doesn't look too good. Build is falling...

Sorry about that. The {#validation-subset} heading ID syntax is Markdown-only — in .mdx files, {...} is parsed as a JSX expression, which caused the acorn parse error. The <a id="validation-subset"></a> tag is actually the correct way to declare a custom anchor in MDX, so it can't be removed. Reverted in 1bd9a6e.

[chrjohn]

@copilot but that causes a conflict with the validation section from the imported configuration doc.
Please rename the whole section to basic validation then and add a link to the complete validation section which is in the imported configuration doc.

[Copilot]

@copilot but that causes a conflict with the validation section from the imported configuration doc.
Please rename the whole section to basic validation then and add a link to the complete validati...

Done in a8b4e8c. Renamed ### Validation → ### Basic Validation (resolves the anchor conflict with ## Validation from the imported reference doc) and added a link: "For the complete list of validation settings, see Validation in the Full Configuration Options reference below." Also removed the <a id="validation-subset"></a> workaround tag that's no longer needed, and updated .gitignore to exclude the fetched _configuration_reference.mdx file (c0e6de7).