Fix Docs search scope to include Node-RED content & improve pagination logic

[Yndira-E]

Description

This PR addresses the issue where documentation under flowfuse.com/node-red/ was not discoverable when searching from the main Docs section.

Previously, the search scope was too narrow. I have updated the Algolia Autocomplete implementation to treat docs and node-red as distinct sources when searching within the documentation area.

I've also refactored the "Load More" Logic:
- The "Load More" button now automatically hides if all available results (nbHits) are already displayed.
- Implemented a state map (hitsPerPageMap) so that clicking "Load More" on the Docs section does not accidentally expand the Node-RED section (and vice versa).
- Replaced the DOM event dispatch hack with the native Algolia refresh() method for reliable reloading.
- The button wasn't working on mobile, so switched to mousedown/touchstart with preventDefault() to ensure the search input retains focus when clicking "Load More"

Related Issue(s)

closes #4193

Checklist

• I have read the contribution guidelines
• I have considered the performance impact of these changes
• Suitable unit/system level tests have been added and they pass
• Documentation has been updated
• For blog PRs, an Art Request has been created (instructions)

[netlify]

✅ Deploy Preview for flowforge-website ready!

Name	Link
🔨 Latest commit	baee786
🔍 Latest deploy log	https://app.netlify.com/projects/flowforge-website/deploys/694592d30d3c54000847de4e
😎 Deploy Preview	https://deploy-preview-4283--flowforge-website.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.
Lighthouse	1 paths audited Performance: 82 (🟢 up 25 from production) Accessibility: 80 (no change from production) Best Practices: 100 (🟢 up 8 from production) SEO: 92 (no change from production) PWA: - View the detailed breakdown and full score reports

---

To edit notification comments on pull requests, go to your Netlify project configuration.