feat(tui): /model and /setup slash commands with in-place CLI handoff

- hermes-ink: export `withInkSuspended()` + `useExternalProcess()` that
  pause/resume Ink around an arbitrary external process (built on the
  existing enterAlternateScreen/exitAlternateScreen plumbing)
- tui: `launchHermesCommand(args)` spawns the `hermes` binary with
  inherited stdio, with `HERMES_BIN` override for non-standard launches
- tui: `/model` and `/setup` slash commands invoke the CLI wizards
  in-place, then re-preflight `setup.status` and auto-start a session on
  success — no more exit-and-relaunch to finish first-run setup
- setup panel now advertises those slashes instead of only pointing
  users back at the shell

ui-tui/packages/hermes-ink/src/entry-exports.ts

@@ -1,3 +1,4 @@
+export { default as TextInput, UncontrolledTextInput } from 'ink-text-input'
 export { default as useStderr } from './hooks/use-stderr.js'
 export { default as useStdout } from './hooks/use-stdout.js'
 export { Ansi } from './ink/Ansi.js'
@@ -12,6 +13,7 @@ export { default as Spacer } from './ink/components/Spacer.js'
 export { default as Text } from './ink/components/Text.js'
 export { default as useApp } from './ink/hooks/use-app.js'
 export { useDeclaredCursor } from './ink/hooks/use-declared-cursor.js'
+export { useExternalProcess, withInkSuspended, type RunExternalProcess } from './ink/hooks/use-external-process.js'
 export { default as useInput } from './ink/hooks/use-input.js'
 export { useHasSelection, useSelection } from './ink/hooks/use-selection.js'
 export { default as useStdin } from './ink/hooks/use-stdin.js'
@@ -22,4 +24,3 @@ export { useTerminalViewport } from './ink/hooks/use-terminal-viewport.js'
 export { default as measureElement } from './ink/measure-element.js'
 export { createRoot, default as render, renderSync } from './ink/root.js'
 export { stringWidth } from './ink/stringWidth.js'
-export { default as TextInput, UncontrolledTextInput } from 'ink-text-input'

ui-tui/packages/hermes-ink/src/ink/hooks/use-external-process.ts

@@ -0,0 +1,27 @@
+import { useCallback } from 'react'
+
+import instances from '../instances.js'
+
+export type RunExternalProcess = () => Promise<void>
+
+export async function withInkSuspended(run: RunExternalProcess): Promise<void> {
+  const ink = instances.get(process.stdout)
+
+  if (!ink) {
+    await run()
+
+    return
+  }
+
+  ink.enterAlternateScreen()
+
+  try {
+    await run()
+  } finally {
+    ink.exitAlternateScreen()
+  }
+}
+
+export function useExternalProcess(): (run: RunExternalProcess) => Promise<void> {
+  return useCallback((run: RunExternalProcess) => withInkSuspended(run), [])
+}