fix(setup): wizard errors copyable above the dialog, CLI skew explained, exec transparency

Field test of the setup wizard surfaced three trust breaks in one run:
an unexplained macOS Documents permission prompt, a perceived crash,
and an error message whose copy button could not be reached.

Root causes and fixes:
- chain init failures were shown as a SnackBar, which lands BEHIND the
  wizard's modal barrier: dimmed, clipped, copy unreachable — and the
  click aimed at it hit the barrier, dismissing the whole wizard with
  all answers (the perceived crash). Errors now open a modal dialog
  ABOVE the wizard via showChainErrorDialog with a copyable detail
  block, and the wizard is no longer barrier-dismissible.
- When the resolved chain binary is older than Studio and rejects
  --plan-json, the wizard now explains the version skew in plain
  language (binary path + update path) instead of leaking a raw clap
  usage error. A missing binary gets its own localized story.
- Step 3 announces which chain binary the preview will execute; when
  that binary physically lives (symlinks resolved) in a TCC-protected
  folder, the wizard pre-explains the macOS folder prompt.

Supporting changes: FriendlyError passes through friendlyError()
unchanged so call sites can ship precise localized stories through the
shared presentation; SystemActions gains resolvedChainBinary() plus
run/resolve test seams; ChainErrorBox hugs its content instead of
filling an unbounded dialog; the wizard's answers file is written
synchronously (the async dart:io variants never complete under the
widget-test fake-async zone).

Verified: flutter analyze clean, 53 tests green (6 new wizard error-
path tests incl. clipboard round-trip), plus a live GUI walk on macOS
in dark + light with a stale binary (skew dialog, copy verified via
clipboard) and with the real binary (TCC pre-explanation with the
resolved path, full plan preview).

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

lib/l10n/app_localizations.dart

@@ -5479,6 +5479,66 @@ abstract class AppLocalizations {
   /// **'The free-text path needs a configured system AI (Settings → System AI). The choices above always work — no AI required.'**
   String get setupFreeTextUnavailable;
 
+  /// No description provided for @setupExecHint.
+  ///
+  /// In en, this message translates to:
+  /// **'For the preview and setup, Studio runs the “chain” program: {path}'**
+  String setupExecHint(String path);
+
+  /// No description provided for @setupExecHintTcc.
+  ///
+  /// In en, this message translates to:
+  /// **'The program lives at {path} — macOS may ask once for access to that folder (e.g. “Documents”). That is expected and fine.'**
+  String setupExecHintTcc(String path);
+
+  /// No description provided for @setupNoBinaryStepHint.
+  ///
+  /// In en, this message translates to:
+  /// **'The “chain” program could not be found on this machine — the preview in the next step will fail. You can pick it under “Doctor”, or install Ch∆In.'**
+  String get setupNoBinaryStepHint;
+
+  /// No description provided for @setupNoBinary.
+  ///
+  /// In en, this message translates to:
+  /// **'The “chain” program could not be found on this machine.'**
+  String get setupNoBinary;
+
+  /// No description provided for @setupNoBinaryHint.
+  ///
+  /// In en, this message translates to:
+  /// **'Without it the assistant cannot apply the setup. Pick it under “Doctor”, or reinstall Ch∆In.'**
+  String get setupNoBinaryHint;
+
+  /// No description provided for @setupCliTooOld.
+  ///
+  /// In en, this message translates to:
+  /// **'The installed “chain” program is older than Studio and does not know this assistant yet.'**
+  String get setupCliTooOld;
+
+  /// No description provided for @setupCliTooOldHint.
+  ///
+  /// In en, this message translates to:
+  /// **'Found: {path}. Please update Ch∆In (“Doctor” page → update, or in a terminal: chain update apply) and reopen the assistant afterwards.'**
+  String setupCliTooOldHint(String path);
+
+  /// No description provided for @setupPreviewFailed.
+  ///
+  /// In en, this message translates to:
+  /// **'The plan preview could not be created — the “chain” program reported an error.'**
+  String get setupPreviewFailed;
+
+  /// No description provided for @setupApplyFailed.
+  ///
+  /// In en, this message translates to:
+  /// **'The setup could not be applied — the “chain” program reported an error.'**
+  String get setupApplyFailed;
+
+  /// No description provided for @setupCliUsedBinary.
+  ///
+  /// In en, this message translates to:
+  /// **'Executed: {path}'**
+  String setupCliUsedBinary(String path);
+
   /// No description provided for @setupFreeTextParseError.
   ///
   /// In en, this message translates to: