This updates the remaining stale auth hook references after the auth
hooks guide moved from hash anchors to dedicated subpages.
It switches the RBAC guide to the current custom access token hook page,
updates the MFA verification hook reference in both the docs error-code
source and the shared-data export, and fixes the matching custom access
token hook comments in the Slack Clone SQL examples.
Testing: not run. Link-target updates only.
Refs #46947
<!-- This is an auto-generated comment: release notes by coderabbit.ai
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## Summary by CodeRabbit
## Release Notes
* **Documentation**
* Updated error code and auth hook documentation reference links to
point to more specific canonical documentation pages, improving accuracy
of references for developers.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
## I have read the
[CONTRIBUTING.md](https://github.com/supabase/supabase/blob/master/CONTRIBUTING.md)
file.
YES
## What kind of change does this PR introduce?
This is something we've discussed for a while. A shared place for error
codes and their mappings, descriptors etc. Available for all projects in
the monorepo.
Peter Chen J.