feat(studio): guided-setup wizard (reuses chain init engine)

A Welcome 'Setup assistant' button opens a wizard that collects
scenario / intent / target (+ approval & data-local toggles), then calls
`chain init --answers` to preview the assembled plan and `--apply --force`
to write the config — reusing the Rust deterministic engine, no logic
duplicated. New SystemActions.chainInit; copyable errors via
showFaiProcessError; EN+DE l10n. analyze clean; smoke test + existing
welcome/sidebar tests pass.

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

lib/data/system_actions.dart

@@ -143,6 +143,15 @@ class SystemActions {
     return _runFai(['daemon', ...args]);
   }
 
+  /// Run a `chain init ...` subcommand. Used by the guided-setup
+  /// wizard to preview a plan (`--answers <file>`) and apply it
+  /// (`--answers <file> --apply --force`).
+  static Future<({bool ok, String stdout, String stderr})> chainInit(
+    List<String> args,
+  ) async {
+    return _runFai(['init', ...args]);
+  }
+
   /// Run `chain update apply --channel <c>`. Long-running on a slow
   /// network — caller should show a spinner.
   static Future<({bool ok, String stdout, String stderr})> chainUpdateApply(