Add MCP server (v1 read-only): toggle, per-pane gate, panel UI

src/lib/layout/LeafPane.tsx

@@ -418,6 +418,22 @@ export default function LeafPane({ leaf }: { leaf: LeafNode }) {
           📡
         </button>
 
+        <button
+          className={`bcast-chip mcp-chip${leaf.mcpAllow ? " on" : ""}`}
+          onClick={(e) => {
+            e.stopPropagation();
+            orch.toggleMcpAllow(leaf.id);
+          }}
+          title={
+            leaf.mcpAllow
+              ? "MCP can see this pane — click to revoke"
+              : "MCP cannot see this pane — click to allow (only matters when the MCP server is on)"
+          }
+          aria-pressed={leaf.mcpAllow ? "true" : "false"}
+        >
+          🤖
+        </button>
+
         {isIdle && statusOk ? (
           <span className="pane-status idle" title={`No output for ${IDLE_THRESHOLD_MS / 1000}s+`}>
             idle