DOCS-3814: Expand left sidenav one level down by default to improve navigation and discoverability

[nathan-contino]

Given our tabbed configuration, the 'first level' is actually the third in configuration.
Much AI ink was spilled to discover this one-line change.

[netlify]

✅ Deploy Preview for viam-docs ready!

Name	Link
🔨 Latest commit	50ece97
🔍 Latest deploy log	https://app.netlify.com/sites/viam-docs/deploys/680bf1f8a2cda2000839ceb1
😎 Deploy Preview	https://deploy-preview-4250--viam-docs.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.
Lighthouse	1 paths audited Performance: 34 (🔴 down 5 from production) Accessibility: 100 (no change from production) Best Practices: 100 (no change from production) SEO: 92 (no change from production) PWA: 70 (no change from production) View the detailed breakdown and full score reports

---

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

[JessamyT]

Hmm this does create odd behavior with the expandy arrows (menu-toggle) though--can you make their default state pointing down instead of to the side, so that you don't click once to change the arrow, and click again to collapse?

OR are we okay with no collapsability, i.e. just make them headings (as they were a couple months ago) with no clickability?

Edit: Maybe has something to do with $activePath in sidebar-tree.html??

[nathan-contino]

I think it should be good now! Thanks for noticing this. I got a bit of tunnel vision looking at AI changes for too long.

[JessamyT]

LGTM! I still wonder if any users will actually want to collapse the left nav or if we should just make all top-level items headings without collapsibility (like they were a couple months ago), but that can be decided separately