Phase 7: Agent Selector — per-agent soul.md + ChromaDB memory filtering

- Agent dropdown UI (chip button + hidden select) in composer header
- Session.agent field persists agent selection across refresh
- soul.md loaded per-agent via ephemeral_system_prompt injection
- ChromaDB memory filtered by agent topic (lotus/, sunflower/, etc.)
- Fixed streaming.py: agent→_ai_agent variable shadowing (lines 1161, 1163)
- New API endpoints: /api/agents/topology, /api/agents/memory/search
- Agent metadata registry with emoji, name, description per Tier-2 agent

static/boot.js

@@ -439,6 +439,7 @@ $('modelSelect').onchange=async()=>{
   await api('/api/session/update',{method:'POST',body:JSON.stringify({session_id:S.session.session_id,workspace:S.session.workspace,model:selectedModel})});
   S.session.model=selectedModel;
   if(typeof syncModelChip==='function') syncModelChip();
+  if(typeof syncAgentChip==='function') syncAgentChip();
   syncTopbar();
   // Warn if selected model belongs to a different provider than what Hermes is configured for
   if(typeof _checkProviderMismatch==='function'){