feat(setup): first-run gate, hub-first preview, honest wording — setup before the app

Stefan's live findings, all four addressed at the root:

- 'In 3 Fragen loslegen' read like ad copy → the entry is now plainly
  'Einrichtung starten' / 'Start setup'.
- The setup button sat permanently on the Welcome page of a running
  app ('setup after the app runs is backwards' — reported twice). A
  fresh install now starts INSIDE the setup: SetupGateScreen hosts
  the wizard embedded as the page (new embedded/onFinished modes on
  GuidedSetupDialog), with an explicit 'Später einrichten' skip.
  Welcome loses the setup button entirely and stays a calm intro.
- Re-running the setup later lives in Settings → General ('Run setup
  again…'), the single post-first-run home.
- 'You must grant access first and only then see what will be done':
  the preview used to spawn the chain CLI, whose first run could pop
  the macOS permission prompt BEFORE the plan was ever shown. The
  preview now calls the new PlanSetup RPC over the live hub
  connection (no subprocess, nothing granted); the CLI remains only
  a fallback when no hub is reachable — and applying stays the
  explicit, separate step.

Widget tests: gate hosts the wizard + skip/cancel leave it; CLI-path
tests drive the fallback through the new hub-preview test seam.
Suite 76 green, analyze clean.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/l10n/app_en.arb

@@ -1830,7 +1830,11 @@
   "setupSigPublicStoreNotice": "This setup only accepts signed modules. The public store currently ships unsigned bundles — the prepared modules therefore come from your own, signed source.",
   "setupAllowUnsigned": "Allow installing from the public store",
   "setupAllowUnsignedSub": "Deliberately relaxes the signature requirement. Fine for trying things out — re-enable it for regulated operation.",
-  "setupStartCta": "Get started in 3 questions",
+  "setupStartCta": "Start setup",
+  "setupGateIntro": "Before you start: three questions, then Ch∆In sets this machine up to match. Nothing changes without your confirmation.",
+  "setupGateSkip": "Set up later",
+  "settingsRunSetup": "Run setup again…",
+  "settingsRunSetupHint": "Opens the setup assistant (three questions, preview, apply). Your existing configuration is only replaced after you confirm.",
   "setupPlanRunbookLocal": "This machine is being set up; the hub runs locally and starts on demand.",
   "setupPlanRunbookService": "This machine is being set up: the hub will start automatically on boot (background service). For a different server, run the setup there.",
   "setupPlanRunbookAirgap": "Intended for an isolated server without internet — modules and updates arrive as offline bundles.",