Migrate CLI E2E tests to Node.js 26

Run the CLI subprocess suites and benchmark tools as native TypeScript with
node:test, and move them under test/e2e-cli.

Update CI and Compose runners, run local smoke tests on Linux, macOS, and
Windows, and collect source-mapped CLI coverage with c8.

test/e2e-cli/helpers/env.ts

@@ -0,0 +1,27 @@
+import { readFile } from "node:fs/promises";
+/**
+ * Load a .env-style file (KEY=value per line) into a plain object.
+ * Equivalent to `source $TEST_ENV_FILE; set -a` in bash.
+ * Maybe we should use some library... now it is just the minimal implementation that covers our use cases.
+ *
+ * Supported value formats:
+ *   KEY=value
+ *   KEY='single quoted'
+ *   KEY="double quoted"
+ *   # comment lines are ignored
+ */
+export async function loadEnvFile(filePath: string): Promise<Record<string, string>> {
+    const text = await readFile(filePath, "utf8");
+    const result: Record<string, string> = {};
+    for (const line of text.split("\n")) {
+        const trimmed = line.trim();
+        if (!trimmed || trimmed.startsWith("#")) continue;
+        const idx = trimmed.indexOf("=");
+        if (idx < 0) continue;
+        const key = trimmed.slice(0, idx).trim();
+        const raw = trimmed.slice(idx + 1).trim();
+        // Strip surrounding single or double quotes
+        result[key] = raw.replace(/^(['"])(.*)\1$/, "$2");
+    }
+    return result;
+}