feat: port CLI, TUI, and launcher from v1.5 into v2 (#1452)

Ports the CLI, TUI, and launcher from v1.5 into v2 behind a single
`mcp-inspector` entrypoint (launcher → web/cli/tui). Includes the
`mcp-inspector --web --dev` launcher fix (Vite alias resolution + prod-server
double-start), the root `postinstall` install cascade with simplified CI, and
spec/AGENTS docs (no-workspaces rationale, Development setup).

Closes #1246.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/cli/__tests__/helpers/assertions.test.ts

@@ -0,0 +1,42 @@
+import { describe, it, expect } from "vitest";
+import { expectCliSuccess, expectCliFailure } from "./assertions.js";
+import type { CliResult } from "./cli-runner.js";
+
+function assertionMessage(fn: () => void): string {
+  try {
+    fn();
+    return "";
+  } catch (error) {
+    return error instanceof Error ? error.message : String(error);
+  }
+}
+
+describe("CLI assertion helpers", () => {
+  it("expectCliSuccess includes stdout and stderr on failure", () => {
+    const result: CliResult = {
+      exitCode: 1,
+      stdout: "tool output",
+      stderr: "connect error",
+      output: "tool outputconnect error",
+    };
+
+    const message = assertionMessage(() => expectCliSuccess(result));
+    expect(message).toContain("CLI exited with code 1");
+    expect(message).toContain("stdout: tool output");
+    expect(message).toContain("stderr: connect error");
+  });
+
+  it("expectCliFailure includes stdout and stderr on unexpected success", () => {
+    const result: CliResult = {
+      exitCode: 0,
+      stdout: "ok",
+      stderr: "",
+      output: "ok",
+    };
+
+    const message = assertionMessage(() => expectCliFailure(result));
+    expect(message).toContain("CLI unexpectedly exited with code 0");
+    expect(message).toContain("stdout: ok");
+    expect(message).toContain("stderr: (empty)");
+  });
+});