Docs: use relative links instead of docs.hubsfoundation.org

[HussainAther]

What?

Replaces hard-coded https://docs.hubsfoundation.org/... links in a small set of documentation pages with relative links (e.g. ./beginners-guide-to-CE.html#..., ./hubs-features.html, etc.) so links remain portable across different deployments/hosts.

Files touched:

• docs/how-to-backup-your-Hubs-instance.md
• docs/dev-contributing.md
• docs/dev-client-networking.md
• docs/set-up-SMTP-email-service.md

Why?

• Avoids coupling internal documentation links to a specific production domain.
• Improves portability for forks/self-hosted docs and local preview builds.
• Moves toward consistency with other internal-link patterns already used in the repo.

Examples

Before:

• https://docs.hubsfoundation.org/beginners-guide-to-CE.html#12-generate-your-config-file
• https://docs.hubsfoundation.org/hubs-features.html

After:

• ./beginners-guide-to-CE.html#12-generate-your-config-file
• ./hubs-features.html

How to test

1. Run the docs site locally:

   • cd website
   • npm ci (or yarn if that’s the repo standard)
   • npm start

2. Open the affected pages and click the changed links:

   • “How to backup your Hubs instance”
   • “Contributing”
   • “Client networking”
   • “Set up SMTP email service”

3. Verify links still navigate correctly (including anchors like #12-generate-your-config-file).

Documentation of functionality

No functional behavior changes. This is documentation-only link formatting.

Limitations

• This PR updates only a small subset of pages (those currently containing https://docs.hubsfoundation.org/... links).
• Does not attempt to establish or enforce a repo-wide link style rule by itself.

Alternatives considered

• Leave absolute links as-is (keeps current behavior but remains domain-coupled).
• Normalize all docs links in one sweep (likely better done after a link-format consensus/style guide update).

Open questions

• Should we prefer relative ./page.html links everywhere, or allow .md (since Docusaurus resolves both)?
• Should external absolute links be reserved only for truly external sites?

Additional details or related context

Related to ongoing discussion about standardizing hubs-docs internal link formatting (relative vs absolute) (e.g. issue #254 / link-style discussion).