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_en.arb

@@ -33,6 +33,20 @@
   "welcomeDocApprovalsTitle": "Approvals",
   "welcomeDocApprovalsBlurb": "Human-in-the-loop checkpoints — when to use them, how the audit log records them.",
   "helpTooltip": "Help",
+  "errApprovalRejected": "Approval rejected by reviewer.",
+  "errApprovalRejectedHint": "The reviewer marked this step as rejected. Check the audit log for the reviewer's reason.",
+  "errApprovalTimedOut": "Approval timed out.",
+  "errApprovalTimedOutHint": "No reviewer decided within the configured time. Raise `timeout_seconds` on the approval step or alert the reviewer.",
+  "errOutputTooLarge": "Step output exceeded the size limit.",
+  "errOutputTooLargeHint": "Either trim the output (truncate text, downsample bytes) or raise `max_output_size_mb` in the operator config.",
+  "errServiceUnavailableForStep": "Host service not configured.",
+  "errServiceUnavailableForStepHint": "The module requires a service (e.g. ollama, playwright) the operator hasn't declared. Add it under `services:` in ~/.fai/config.yaml.",
+  "errMissingValue": "Required value is missing.",
+  "errMissingValueHint": "The step expected an input that wasn't wired up — either supply it at run time or fix the upstream `$ref`.",
+  "errMcpUnreachable": "MCP endpoint unreachable.",
+  "errMcpUnreachableHint": "The MCP server didn't respond. Check the endpoint in Settings → Integrations and confirm it's running.",
+  "errCapabilityNotInstalled": "Required capability is not installed.",
+  "errCapabilityNotInstalledHint": "Open the flow's Text tab — the analyzer's Fix button installs the capability if it's in the store.",
   "welcomeDocClose": "Close",
   "welcomeDocFailedToLoad": "Could not load documentation: {error}",
   "@welcomeDocFailedToLoad": {