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

api/agents.py

@@ -1067,3 +1067,40 @@ def _search_all_agents_memory(query: str, limit: int = 20) -> list:
         return matches
     except Exception:
         return []
+
+
+# ── Topology Graph ───────────────────────────────────────────────────────────
+
+def _get_topology() -> dict:
+    """
+    Build a network graph of all agents and their connections.
+    Returns {nodes: [...], edges: [...]} for D3.js visualization.
+    """
+    # Nodes: Rose + all Tier-2 agents
+    nodes = [
+        {"id": "rose", "name": "Rose 🌹", "type": "orchestrator",
+         "color": "#f44336", "domain": "Orchestrator"},
+    ]
+    for agent_id, meta in TIER2_AGENTS.items():
+        nodes.append({
+            "id": agent_id,
+            "name": f"{meta['emoji']} {meta['name']}",
+            "type": "tier2",
+            "color": meta["color"],
+            "domain": meta["domain"],
+        })
+
+    # Edges: Rose connects to all Tier-2 agents
+    edges = []
+    for agent_id in TIER2_AGENTS:
+        edges.append({
+            "source": "rose", "target": agent_id,
+            "type": "orchestrates", "strength": 1,
+        })
+
+    return {"nodes": nodes, "edges": edges}
+
+
+def get_topology() -> dict:
+    """API: GET /api/agents/topology — return agent network graph."""
+    return _get_topology()