fix(mdx): Propagate ENOENT error code for missing MDX files

[seer-by-sentry]

DESCRIBE YOUR PR

The root cause analysis for DOCS-9WX identified that the Page Server Component (/[[...path]]) was throwing an unhandled error when a request for a valid slug (like /changelog) was made, but the corresponding MDX source file was not found at runtime.

This happened because getFileBySlug() in src/mdx.ts was throwing a generic Error object without a .code property when it failed to find a source file. The page.tsx component's catch block, however, specifically checks for e.code === 'ENOENT' to gracefully return notFound(). Since the error lacked this property, it was re-thrown and became an unhandled error.

This fix modifies getFileBySlug() to attach code: 'ENOENT' to the error object when a source file cannot be found. This ensures that the page.tsx component can correctly identify and handle the "file not found" scenario, preventing unhandled errors and returning a proper 404 response.

Resolves DOCS-9WX

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Project	Deployment	Review	Updated (UTC)
develop-docs	Ready	Preview, Comment	Jan 15, 2026 11:09pm
sentry-docs	Ready	Preview, Comment	Jan 15, 2026 11:09pm