Add missing Connectors and Use cases links to docs page navigation

[babltiga]

What changed

The docs page (website/docs/index.html) header navigation had drifted behind the main marketing page: the Connectors (#connectors) and Use cases (#use-cases) sections added to website/index.html were missing from the docs page nav. This adds the two links (as ../index.html#anchor, matching the existing sibling links) in:

• the desktop header nav (nav.nav-links)
• the mobile menu panel (nav.nav-mobile-panel)
• the footer Product column — same drift there: the main footer lists Use cases but the docs footer omitted it (the main footer intentionally has no Connectors entry, so only Use cases is added there)

Link order matches the main page: Features, Connectors, How it works, Use cases, Install, Roadmap, Docs.

Why

Keeps website/docs/index.html in parity with website/index.html per the website-drift rule in CLAUDE.md.

Notes for the reviewer

• Static HTML only, no build step; the diff is exactly 5 inserted <a> lines.
• Verified both target anchors exist on the main page and that the edited file still parses tag-balanced.