fix: enforce .js import extensions via biome project domain

The `useImportExtensions` rule was configured but never ran because the
biome `project` domain wasn't enabled. Enable it for `packages/core/**`
and fix the 3 existing violations (2 extensionless `import type`, 1 bare
directory import) that could cause ESM runtime crashes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: harijoe

biome.json

@@ -57,8 +57,12 @@
     {
       "includes": ["packages/core/**"],
       "linter": {
+        "domains": {
+          "project": "all"
+        },
         "rules": {
           "correctness": {
+            "noUnresolvedImports": "off",
             "useImportExtensions": {
               "level": "error",
               "options": {

packages/core/src/server/express.test.ts

@@ -1,7 +1,7 @@
 import http from "node:http";
 import type { ErrorRequestHandler, RequestHandler } from "express";
 import { afterEach, describe, expect, it, vi } from "vitest";
-import type { McpServer } from "./server";
+import type { McpServer } from "./server.js";
 
 vi.mock("@skybridge/devtools", () => ({
   devtoolsStaticServer: () =>

packages/core/src/server/express.ts

@@ -3,7 +3,7 @@ import path from "node:path";
 import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js";
 import cors from "cors";
 import express from "express";
-import type { McpServer } from "./server";
+import type { McpServer } from "./server.js";
 
 function applyMiddlewares(
   app: express.Express,

packages/core/src/version.ts

@@ -1,6 +1,7 @@
 import { createRequire } from "node:module";
 
 const require = createRequire(import.meta.url);
+// biome-ignore lint/correctness/useImportExtensions: CJS require() for JSON, not an ESM import
 const pkg = require("../package.json") as { version: string };
 
 export const VERSION: string = pkg.version;

packages/core/src/web/components/modal-provider.tsx

@@ -1,5 +1,5 @@
 import { type ReactNode, useEffect, useSyncExternalStore } from "react";
-import { McpAppAdaptor } from "../bridges";
+import { McpAppAdaptor } from "../bridges/index.js";
 
 const modalStyles = `
 .sb-modal-backdrop {