docs: link backup & recovery docs

[paolodamico]

Note

Low Risk
Doc-only changes (module and error documentation) with no functional or behavioral impact.

Overview
Adds central Backup & Recovery documentation links and clearer module-level docs in backup/mod.rs, including references for architecture/threat model and service rejection reasons.

Removes redundant crate-root backup module doc comments from lib.rs and tweaks a factor-management docstring for clarity.

^{Reviewed by Cursor Bugbot for commit ee98c42. Bugbot is set up for automated code reviews on this repo. Configure here.}

[Copilot]

Pull request overview

Updates Bedrock’s backup module documentation to point readers to centralized “Backup & Recovery” docs and reduce redundant crate-root docs.

Changes:

• Add module-level docs and central documentation link in backup/mod.rs.
• Add a pointer to centralized “service rejects” error documentation for BackupError.
• Remove redundant backup module docs from lib.rs.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
bedrock/src/lib.rs	Removes redundant crate-root backup module docs.
bedrock/src/backup/mod.rs	Adds module-level docs and links to centralized Backup & Recovery documentation and error details.