feat(FN-3878): add restore-merge-sha script for commitSha restoration

Adds a new merge commitSha restoration script (`scripts/restore-merge-sha-fn-3878.mjs`) with test coverage to handle a specific FN-3878 merge case, along with a changeset for publishing and a minor plugin vitest config governance alignment across three plugins.

Fusion-Task-Id: FN-3878

plugins/fusion-plugin-even-cards/vitest.config.ts

@@ -0,0 +1,23 @@
+import { fileURLToPath } from "node:url";
+import { defineConfig } from "vitest/config";
+import { computeMaxWorkers } from "../../packages/core/src/__test-utils__/vitest-workers";
+
+const maxWorkers = computeMaxWorkers();
+
+export default defineConfig({
+  resolve: {
+    alias: {
+      "@fusion/core": fileURLToPath(new URL("../../packages/core/src/index.ts", import.meta.url)),
+      "@fusion/plugin-sdk": fileURLToPath(new URL("../../packages/plugin-sdk/src/index.ts", import.meta.url)),
+    },
+  },
+  test: {
+    environment: "node",
+    include: ["src/__tests__/**/*.test.ts"],
+    setupFiles: [fileURLToPath(new URL("../../packages/core/src/__test-utils__/vitest-setup.ts", import.meta.url))],
+    globalSetup: [fileURLToPath(new URL("../../packages/core/src/__test-utils__/vitest-teardown.ts", import.meta.url))],
+    pool: "threads",
+    maxWorkers,
+    poolOptions: { threads: { minThreads: 1, maxThreads: maxWorkers }, forks: { minForks: 1, maxForks: maxWorkers } },
+  },
+});