Add CLI dispatcher and bin entry

Top-level run(argv,{out,err}) accepts an injectable output sink so
handlers can be unit-tested without spawning a subprocess. Handler
map is empty for now; subcommands are wired in as they land.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/cli.test.js

@@ -0,0 +1,46 @@
+'use strict';
+
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const { run } = require('../src/cli');
+
+class Sink {
+  constructor() { this.chunks = []; }
+  write(s) { this.chunks.push(s); }
+  get text() { return this.chunks.join(''); }
+}
+
+test('cli: no args prints usage to stderr, exit 1', () => {
+  const out = new Sink(); const err = new Sink();
+  const code = run([], { out, err });
+  assert.equal(code, 1);
+  assert.match(err.text, /usage/i);
+  assert.match(err.text, /encode/);
+  assert.match(err.text, /decode/);
+  assert.match(err.text, /build/);
+  assert.match(err.text, /inspect/);
+  assert.equal(out.text, '');
+});
+
+test('cli: --help prints usage to stdout, exit 0', () => {
+  const out = new Sink(); const err = new Sink();
+  const code = run(['--help'], { out, err });
+  assert.equal(code, 0);
+  assert.match(out.text, /usage/i);
+  assert.equal(err.text, '');
+});
+
+test('cli: -h alias for --help', () => {
+  const out = new Sink(); const err = new Sink();
+  const code = run(['-h'], { out, err });
+  assert.equal(code, 0);
+  assert.match(out.text, /usage/i);
+});
+
+test('cli: unknown subcommand goes to stderr, exit 1', () => {
+  const out = new Sink(); const err = new Sink();
+  const code = run(['frobnicate'], { out, err });
+  assert.equal(code, 1);
+  assert.match(err.text, /unknown subcommand/i);
+  assert.match(err.text, /frobnicate/);
+});