feat(studio): friendlyError catches hub-specific patterns

Generic gRPC-code mapping was right but not specific enough.
A flow failing with an approval-timeout used to land on
'Deadline exceeded — try again later'; now it reads 'Freigabe-
Timeout abgelaufen — entweder timeout_seconds erhöhen oder
den Reviewer informieren.'

New pattern matchers in _matchHubPattern, runs before the
gRPC-code switch. Six FlowExecutionError shapes covered:

  - approval rejected ("rejected by")
  - approval timeout
  - output too large ("exceeding the X MB cap")
  - host service not declared
  - missing value reference
  - MCP endpoint unreachable
  - capability not installed (NotFound fallback)

Every match comes with a localised hint pointing at the
concrete fix path (audit log / timeout config / Integrations
panel / Text-tab Fix button).

Five new tests pin the matchers — would catch a silent
regression when the hub renames a variant Display string.
All 11 friendly_error tests + 19 Studio tests green.

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

lib/l10n/app_localizations_en.dart

@@ -111,6 +111,56 @@ class AppLocalizationsEn extends AppLocalizations {
   @override
   String get helpTooltip => 'Help';
 
+  @override
+  String get errApprovalRejected => 'Approval rejected by reviewer.';
+
+  @override
+  String get errApprovalRejectedHint =>
+      'The reviewer marked this step as rejected. Check the audit log for the reviewer\'s reason.';
+
+  @override
+  String get errApprovalTimedOut => 'Approval timed out.';
+
+  @override
+  String get errApprovalTimedOutHint =>
+      'No reviewer decided within the configured time. Raise `timeout_seconds` on the approval step or alert the reviewer.';
+
+  @override
+  String get errOutputTooLarge => 'Step output exceeded the size limit.';
+
+  @override
+  String get errOutputTooLargeHint =>
+      'Either trim the output (truncate text, downsample bytes) or raise `max_output_size_mb` in the operator config.';
+
+  @override
+  String get errServiceUnavailableForStep => 'Host service not configured.';
+
+  @override
+  String get errServiceUnavailableForStepHint =>
+      'The module requires a service (e.g. ollama, playwright) the operator hasn\'t declared. Add it under `services:` in ~/.fai/config.yaml.';
+
+  @override
+  String get errMissingValue => 'Required value is missing.';
+
+  @override
+  String get errMissingValueHint =>
+      'The step expected an input that wasn\'t wired up — either supply it at run time or fix the upstream `\$ref`.';
+
+  @override
+  String get errMcpUnreachable => 'MCP endpoint unreachable.';
+
+  @override
+  String get errMcpUnreachableHint =>
+      'The MCP server didn\'t respond. Check the endpoint in Settings → Integrations and confirm it\'s running.';
+
+  @override
+  String get errCapabilityNotInstalled =>
+      'Required capability is not installed.';
+
+  @override
+  String get errCapabilityNotInstalledHint =>
+      'Open the flow\'s Text tab — the analyzer\'s Fix button installs the capability if it\'s in the store.';
+
   @override
   String get welcomeDocClose => 'Close';