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/app/slash/registry.ts

@@ -1,9 +1,10 @@
 import { coreCommands } from './commands/core.js'
 import { opsCommands } from './commands/ops.js'
 import { sessionCommands } from './commands/session.js'
+import { setupCommands } from './commands/setup.js'
 import type { SlashCommand } from './types.js'
 
-export const SLASH_COMMANDS: SlashCommand[] = [...coreCommands, ...sessionCommands, ...opsCommands]
+export const SLASH_COMMANDS: SlashCommand[] = [...coreCommands, ...sessionCommands, ...opsCommands, ...setupCommands]
 
 const byName = new Map<string, SlashCommand>(
   SLASH_COMMANDS.flatMap(cmd => [cmd.name, ...(cmd.aliases ?? [])].map(name => [name, cmd] as const))