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/commands/setup.ts

@@ -0,0 +1,33 @@
+import { withInkSuspended } from '@hermes/ink'
+
+import { launchHermesCommand } from '../../../lib/externalCli.js'
+import { runExternalSetup } from '../../setupHandoff.js'
+import type { SlashCommand } from '../types.js'
+
+export const setupCommands: SlashCommand[] = [
+  {
+    aliases: ['provider'],
+    help: 'configure LLM provider and model (launches `hermes model`)',
+    name: 'model',
+    run: (_arg, ctx) =>
+      void runExternalSetup({
+        args: ['model'],
+        ctx,
+        done: 'provider updated — starting session…',
+        launcher: launchHermesCommand,
+        suspend: withInkSuspended
+      })
+  },
+  {
+    help: 'run full setup wizard (launches `hermes setup`)',
+    name: 'setup',
+    run: (arg, ctx) =>
+      void runExternalSetup({
+        args: ['setup', ...arg.split(/\s+/).filter(Boolean)],
+        ctx,
+        done: 'setup complete — starting session…',
+        launcher: launchHermesCommand,
+        suspend: withInkSuspended
+      })
+  }
+]

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))