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/src/content/setup.ts

@@ -8,11 +8,10 @@ export const buildSetupRequiredSections = (): PanelSection[] => [
   },
   {
     rows: [
-      ['1.', 'Exit with Ctrl+C'],
-      ['2.', 'Run `hermes model` to choose a provider + model'],
-      ['3.', 'Or run `hermes setup` for full first-time setup'],
-      ['4.', 'Re-open `hermes --tui` when setup is done']
+      ['/model', 'configure provider + model in-place'],
+      ['/setup', 'run full first-time setup wizard in-place'],
+      ['Ctrl+C', 'exit and run `hermes setup` manually']
     ],
-    title: 'Next Steps'
+    title: 'Actions'
   }
 ]