fix(FN-3789): add @fusion/dashboard to REQUIRED_BUILD_PACKAGES

@fusion/desktop tests dynamically import('@fusion/dashboard') in
local-runtime.ts. When packages/dashboard/dist/index.js is absent
(fresh checkout, merger verification env, CI without an explicit
dashboard build) Vite fails with 'Failed to resolve entry for package
@fusion/dashboard' before the desktop vitest alias takes effect.

scripts/ensure-test-artifacts.mjs is the canonical bootstrap layer
that pnpm test calls before running suites; register @fusion/dashboard
there so the dist is built on demand. Extends node:test coverage
mirroring the hermes/openclaw patterns.

Unblocks: FN-3789, FN-3793, FN-3795, FN-3803 (and any future task
whose merger verification path runs desktop tests).

scripts/__tests__/ensure-test-artifacts.test.mjs

@@ -36,6 +36,27 @@ test("ensureTestArtifacts builds only missing packages", () => {
   assert.deepEqual(calls[0].args, ["--filter", "@fusion-plugin-examples/openclaw-runtime", "build"]);
 });
 
+test("detectMissingArtifacts flags @fusion/dashboard when dist/index.js is missing", () => {
+  const missing = detectMissingArtifacts("/repo", (fullPath) => !fullPath.endsWith("packages/dashboard/dist/index.js"));
+  const names = missing.map((pkg) => pkg.name);
+
+  assert.ok(names.includes("@fusion/dashboard"));
+});
+
+test("ensureTestArtifacts rebuilds @fusion/dashboard when its dist is missing", () => {
+  const calls = [];
+  const built = ensureTestArtifacts(
+    "/repo",
+    (cmd, args, cwd) => calls.push({ cmd, args, cwd }),
+    (fullPath) => !fullPath.endsWith("packages/dashboard/dist/index.js"),
+  );
+
+  assert.deepEqual(built, ["@fusion/dashboard"]);
+  assert.equal(calls.length, 1);
+  assert.equal(calls[0].cmd, "pnpm");
+  assert.deepEqual(calls[0].args, ["--filter", "@fusion/dashboard", "build"]);
+});
+
 test("detectMissingArtifacts flags hermes when dist/index.js exists but dist/cli-spawn.js is missing", () => {
   const missing = detectMissingArtifacts("/repo", (fullPath) => !fullPath.endsWith("dist/cli-spawn.js"));
   const names = missing.map((pkg) => pkg.name);