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

src/lib/layout/LeafPane.css

@@ -123,6 +123,12 @@
   color: #f0c060;
   border-color: #c98a1f;
 }
+.bcast-chip.mcp-chip.on {
+  /* Green for MCP-allowed — clearly distinct from broadcast's orange. */
+  background: #1a3a1a;
+  color: #80e080;
+  border-color: #2a6a2a;
+}
 
 .distro-menu {
   position: absolute;

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

src/lib/layout/orchestration.tsx

@@ -31,6 +31,9 @@ export interface Orchestration {
   setShell: (leafId: NodeId, spec: LeafShellSpec) => void;
   setLabel: (leafId: NodeId, label: string | undefined) => void;
   toggleBroadcast: (leafId: NodeId) => void;
+  /** Flip the per-pane mcpAllow flag. Default-deny; chip in the pane
+   *  toolbar drives this. */
+  toggleMcpAllow: (leafId: NodeId) => void;
 
   // SSH host management
   openHostManager: () => void;