opentui(phase3): launcher integration — HERMES_TUI_ENGINE dual-engine

hermes --tui launches the native OpenTUI engine (Bun) when
HERMES_TUI_ENGINE=opentui (env) or display.tui_engine=opentui (config);
Ink stays the default and the shipping path is untouched.

- _resolve_tui_engine() (env > config > ink); refuses opentui on
  Windows/Termux (no Bun) -> falls back to ink with a notice.
- _make_opentui_argv() -> [bun, src/entry.real.tsx] (no build step).
- _bun_bin() with HERMES_BUN override.
- Branch at top of _make_tui_argv BEFORE _ensure_tui_node (Bun-only host
  must not bootstrap Node).
- Gate _launch_tui NODE_OPTIONS/--max-old-space-size on engine==ink (Bun
  is JSC; the V8 flag errors/ignores).

Verified end-to-end via tmux: real hermes --tui -> Bun -> OpenTUI ->
real Python gateway streamed a real reply. No-flag default still ink.

apps/desktop/electron/windows-child-process.test.cjs

@@ -1,54 +0,0 @@
-'use strict'
-
-const test = require('node:test')
-const assert = require('node:assert/strict')
-const fs = require('node:fs')
-const path = require('node:path')
-
-const ELECTRON_DIR = __dirname
-
-function readElectronFile(name) {
-  return fs.readFileSync(path.join(ELECTRON_DIR, name), 'utf8').replace(/\r\n/g, '\n')
-}
-
-function requireHiddenChildOptions(source, needle) {
-  const index = source.indexOf(needle)
-  assert.notEqual(index, -1, `missing call site: ${needle}`)
-  const snippet = source.slice(index, index + 700)
-  assert.match(
-    snippet,
-    /hiddenWindowsChildOptions\(/,
-    `expected ${needle} to wrap child-process options with hiddenWindowsChildOptions`
-  )
-}
-
-test('desktop background child processes opt into hidden Windows consoles', () => {
-  const source = readElectronFile('main.cjs')
-
-  assert.match(source, /function hiddenWindowsChildOptions\(options = \{\}\)/)
-
-  requireHiddenChildOptions(source, "execFileSync(\n          'reg'")
-  requireHiddenChildOptions(source, 'execFileSync(pyExe')
-  requireHiddenChildOptions(source, 'spawn(resolveGitBinary()')
-  requireHiddenChildOptions(source, "execFileSync('taskkill'")
-  requireHiddenChildOptions(source, 'spawn(command, args')
-  requireHiddenChildOptions(source, "spawn('curl'")
-  requireHiddenChildOptions(source, 'spawn(backend.command, backend.args')
-  requireHiddenChildOptions(source, 'hermesProcess = spawn(backend.command, backend.args')
-  requireHiddenChildOptions(source, "spawn(py, ['-m', 'hermes_cli.main', 'uninstall', '--gui-summary']")
-})
-
-test('intentional or interactive desktop child processes stay documented', () => {
-  const source = readElectronFile('main.cjs')
-
-  assert.match(source, /windowsHide: false/)
-  assert.match(source, /nodePty\.spawn\(command, args/)
-  assert.match(source, /spawn\('cmd\.exe', \['\/c', 'start'/)
-})
-
-test('bootstrap PowerShell runner hides Windows console children', () => {
-  const source = readElectronFile('bootstrap-runner.cjs')
-
-  assert.match(source, /function hiddenWindowsChildOptions\(options = \{\}\)/)
-  requireHiddenChildOptions(source, 'spawn(ps, fullArgs')
-})