fix(docs): Prevent unhandled error for invalid library IDs in docs head()

[sentry]

This PR addresses an issue where navigating to documentation URLs with invalid library IDs (e.g., /select/latest/...) resulted in an unhandled error during hydration, instead of a graceful 404.

Root Cause:
The head() function in src/routes/_library/$libraryId/$version.docs.framework.$framework.$.tsx was calling getLibrary(libraryId). The getLibrary() utility throws an error if the provided libraryId does not exist. While the parent route (/_library/$libraryId/route.tsx) correctly uses findLibrary() and throws notFound() for invalid IDs, TanStack Router's hydration process still evaluates the child route's head() function, leading to the unhandled error.

Solution:

1. Updated the imports in src/routes/_library/$libraryId/$version.docs.framework.$framework.$.tsx to include findLibrary and notFound.
2. Modified the head() function in the same file to use findLibrary(libraryId) instead of getLibrary(libraryId).
3. Added a conditional check: if findLibrary returns undefined (meaning the library was not found), throw notFound() is called. This aligns the behavior with sibling routes (e.g., src/routes/_library/$libraryId/$version.docs.$.tsx) and ensures that invalid library IDs are handled gracefully, resulting in a proper 404 page.

Fixes TANSTACK-COM-45W

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	tanstack-com	e525d95	Commit Preview URL Branch Preview URL	Aug 31 2026, 11:06 PM