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.ts

@@ -0,0 +1,64 @@
+import { expect } from "vitest";
+import type { CliResult } from "./cli-runner.js";
+
+function formatCliOutput(result: CliResult): string {
+  const out = result.stdout?.trim() || "(empty)";
+  const err = result.stderr?.trim() || "(empty)";
+  return `stdout: ${out}\nstderr: ${err}`;
+}
+
+/**
+ * Assert that CLI command succeeded (exit code 0)
+ */
+export function expectCliSuccess(result: CliResult) {
+  expect(
+    result.exitCode,
+    `CLI exited with code ${result.exitCode}. ${formatCliOutput(result)}`,
+  ).toBe(0);
+}
+
+/**
+ * Assert that CLI command failed (non-zero exit code)
+ */
+export function expectCliFailure(result: CliResult) {
+  expect(
+    result.exitCode,
+    `CLI unexpectedly exited with code ${result.exitCode}. ${formatCliOutput(result)}`,
+  ).not.toBe(0);
+}
+
+/**
+ * Assert that output contains expected text
+ */
+export function expectOutputContains(result: CliResult, text: string) {
+  expect(result.output).toContain(text);
+}
+
+/**
+ * Assert that output contains valid JSON
+ * Uses stdout (not stderr) since JSON is written to stdout and warnings go to stderr
+ */
+export function expectValidJson(result: CliResult) {
+  expect(() => JSON.parse(result.stdout)).not.toThrow();
+  return JSON.parse(result.stdout);
+}
+
+/**
+ * Assert that output contains JSON with error flag
+ */
+export function expectJsonError(result: CliResult) {
+  const json = expectValidJson(result);
+  expect(json.isError).toBe(true);
+  return json;
+}
+
+/**
+ * Assert that output contains expected JSON structure
+ */
+export function expectJsonStructure(result: CliResult, expectedKeys: string[]) {
+  const json = expectValidJson(result);
+  expectedKeys.forEach((key) => {
+    expect(json).toHaveProperty(key);
+  });
+  return json;
+}