feat(studio): contextual "Add registry token" CTA on install auth wall (v0.46.0)

The hub's v0.10.91 install error message already tells the
operator exactly what to do — set FAI_REGISTRY_TOKEN or save
to ~/.fai/registry-token via Settings. But that text lives in
a FaiErrorBox inside the install dialog. Reading the buried
recovery instruction, finding Settings, scrolling to the
Registry credentials panel, pasting, then re-clicking the
install pill is five hops for what should be one.

When at least one item in the install dialog fails with the
"registry returned an HTML page" / "no registry token
configured" signature, the dialog now surfaces a prominent
filled "Add registry token" button next to Close. Click closes
the install dialog and opens the Settings dialog directly so
the operator pastes + saves without losing context. After
Settings dismisses, the operator is back at the flow card and
re-clicks the same pill to retry.

Detection is signature-based (substring match on the hub's
error text) so it activates whether the install was a single-
pill click or an "Install all" sequence. Other failure modes
(network down, signature invalid, sha mismatch) still show
just the Close button — the CTA is specific to the auth-wall
case it can actually unblock.

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

lib/l10n/app_localizations.dart

@@ -1958,6 +1958,12 @@ abstract class AppLocalizations {
   /// **'{ok} installed, {failed} failed.'**
   String flowsInstallDepsAnyFailed(int ok, int failed);
 
+  /// No description provided for @flowsInstallAuthWallButton.
+  ///
+  /// In en, this message translates to:
+  /// **'Add registry token'**
+  String get flowsInstallAuthWallButton;
+
   /// No description provided for @flowsOpenInEditorTooltip.
   ///
   /// In en, this message translates to: