fix(approvals): usertest-panel hardening (0.81.0)

Panel findings against the reworked approvals page, fixed in place:

- Never fabricate the request time: ApprovalRecord.createdAt is
  nullable now; a missing created_at omits the line instead of
  rendering DateTime.now() (which drifted on refresh). Guard:
  approvals_origin_test pins the omit-on-null invariant.
- Copyable errors on approve/reject/batch via showChainErrorSnack
  (the hard project rule) — batch surfaces the first real cause.
- Reject requires a reason: ChainInlineHelp strip + confirm disabled
  while empty, no more silent close-and-nothing-happens.
- Batch approve applies the same no-data confirmation as the single
  path, naming how many selected requests carry no show: data.
- Plainer language: glossary "Vorgang (Flow)", history label FRAGE
  (was PROMPT), no-data hint drops developer jargon.
- One-click copy of the run id; history payload pretty-prints like
  the card.

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

lib/data/hub.dart

@@ -1152,7 +1152,13 @@ class HubService {
             stepId: e.stepId,
             prompt: e.prompt,
             payloadPreview: e.payloadPreview.isEmpty ? null : e.payloadPreview,
-            createdAt: DateTime.tryParse(e.createdAt) ?? DateTime.now(),
+            // Never fabricate the request time: a missing / unparseable
+            // created_at stays null so the card can omit the line
+            // instead of showing "now" (which would even change on
+            // every refresh) as if it were the truth.
+            createdAt: e.createdAt.isEmpty
+                ? null
+                : DateTime.tryParse(e.createdAt),
             expiresAt: e.expiresAt.isEmpty
                 ? null
                 : DateTime.tryParse(e.expiresAt),
@@ -1762,7 +1768,11 @@ class ApprovalRecord {
   final String stepId;
   final String prompt;
   final String? payloadPreview;
-  final DateTime createdAt;
+
+  /// When the approval was requested. Null when the hub sent no
+  /// parseable timestamp — the card omits the line rather than
+  /// inventing one.
+  final DateTime? createdAt;
   final DateTime? expiresAt;
 
   /// One of: pending / approved / rejected / expired.