Separate user docs from developer/contributor docs in the IA

[gjong]

Labels: enhancement, information-architecture, priority:P2
Parent issue: Epic: Documentation site overhaul

Problem
Getting Started / How-To / Concepts (end-user docs) sit in the same top-level nav as Architecture / ADRs / API (contributor/integrator docs), which can confuse end users.

Suggested fix

• Add a distinct entry point (e.g., "For contributors" / "Developer docs") separating the two audiences.
• Add a "New here?" onboarding path on the home page: Install → Create user → First account → Categorize.

Acceptance criteria

• Clear visual/structural separation between user docs and developer docs.
• Home page has an explicit onboarding path for new users.