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/cli-runner.ts

@@ -0,0 +1,97 @@
+import { spawn } from "child_process";
+import { resolve } from "path";
+import { fileURLToPath } from "url";
+import { dirname } from "path";
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+const CLI_PATH = resolve(__dirname, "../../build/index.js");
+
+export interface CliResult {
+  exitCode: number | null;
+  stdout: string;
+  stderr: string;
+  output: string; // Combined stdout + stderr
+}
+
+export interface CliOptions {
+  timeout?: number;
+  cwd?: string;
+  env?: Record<string, string>;
+  signal?: AbortSignal;
+}
+
+/**
+ * Run the CLI with given arguments and capture output
+ */
+export async function runCli(
+  args: string[],
+  options: CliOptions = {},
+): Promise<CliResult> {
+  return new Promise((resolve, reject) => {
+    const child = spawn("node", [CLI_PATH, ...args], {
+      stdio: ["pipe", "pipe", "pipe"],
+      cwd: options.cwd,
+      env: { ...process.env, ...options.env },
+      signal: options.signal,
+      // Own process group on Unix so timeout can kill CLI + stdio grandchildren.
+      detached: process.platform !== "win32",
+    });
+
+    let stdout = "";
+    let stderr = "";
+    let resolved = false;
+
+    // Default timeout of 10 seconds (less than vitest's 15s)
+    const timeoutMs = options.timeout ?? 10000;
+    const timeout = setTimeout(() => {
+      if (!resolved) {
+        resolved = true;
+        // Kill the process and all its children
+        try {
+          if (process.platform !== "win32" && child.pid != null) {
+            process.kill(-child.pid, "SIGTERM");
+          } else {
+            child.kill("SIGTERM");
+          }
+        } catch {
+          // Process might already be dead, try direct kill
+          try {
+            child.kill("SIGKILL");
+          } catch {
+            // Process is definitely dead
+          }
+        }
+        reject(new Error(`CLI command timed out after ${timeoutMs}ms`));
+      }
+    }, timeoutMs);
+
+    child.stdout.on("data", (data) => {
+      stdout += data.toString();
+    });
+
+    child.stderr.on("data", (data) => {
+      stderr += data.toString();
+    });
+
+    child.on("close", (code) => {
+      if (!resolved) {
+        resolved = true;
+        clearTimeout(timeout);
+        resolve({
+          exitCode: code,
+          stdout,
+          stderr,
+          output: stdout + stderr,
+        });
+      }
+    });
+
+    child.on("error", (error) => {
+      if (!resolved) {
+        resolved = true;
+        clearTimeout(timeout);
+        reject(error);
+      }
+    });
+  });
+}