fix: route Exa and CodeGraph through shared mcp adapter

extensions/mcp.ts

@@ -0,0 +1,13 @@
+import type { ExtensionAPI } from "@earendil-works/pi-coding-agent";
+import { createMcpAdapter } from "pi-mcp-adapter";
+import { createExaToolApiOverride } from "./exa-tool-prefix.ts";
+import { MCP_CONFIG } from "./mcp-config.ts";
+
+const mcpAdapter = createMcpAdapter({
+	config: MCP_CONFIG,
+});
+
+/** Connect Pi to Exa and CodeGraph through one shared MCP adapter instance. */
+export default function mcpExtension(pi: ExtensionAPI): void {
+	mcpAdapter(createExaToolApiOverride(pi));
+}