feat(studio): Approvals page gains History tab

Pending tab keeps the existing card layout for actionable
approvals. New History tab shows decided rows (approved /
rejected / expired) as compact one-liners, color-coded by
status with reviewer + decided-at metadata. Click expands to
the full record (prompt, payload preview, reason, ids).

Closes the visibility gap from the recent fix: rejected
approvals were correctly written to the hash-chained audit
log but invisible to operators on the Approvals page itself.
HubService gains `listApprovalsRecords(statuses:)` returning
the decided-side fields the Studio wire previously dropped.

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

lib/data/hub.dart

@@ -461,6 +461,42 @@ class HubService {
         .toList();
   }
 
+  /// List approvals filtered by status. Empty [statuses] returns
+  /// every row (pending + decided + expired). Returned records
+  /// carry the decided-side fields so the History tab can render
+  /// "rejected by alice@studio at … because …".
+  Future<List<ApprovalRecord>> listApprovalsRecords({
+    List<String> statuses = const [],
+    int limit = 200,
+  }) async {
+    final entries = await _client.listApprovals(
+      statuses: statuses,
+      limit: limit,
+    );
+    return entries
+        .map(
+          (e) => ApprovalRecord(
+            id: e.approvalId,
+            flowName: e.flowName,
+            stepId: e.stepId,
+            prompt: e.prompt,
+            payloadPreview:
+                e.payloadPreview.isEmpty ? null : e.payloadPreview,
+            createdAt: DateTime.tryParse(e.createdAt) ?? DateTime.now(),
+            expiresAt: e.expiresAt.isEmpty
+                ? null
+                : DateTime.tryParse(e.expiresAt),
+            status: e.status,
+            decidedAt: e.decidedAt.isEmpty
+                ? null
+                : DateTime.tryParse(e.decidedAt),
+            decidedBy: e.decidedBy,
+            reason: e.reason,
+          ),
+        )
+        .toList();
+  }
+
   Future<void> approve(String id, String reviewer) =>
       _client.approve(approvalId: id, reviewer: reviewer);
 
@@ -695,6 +731,41 @@ class PendingApproval {
   });
 }
 
+/// Full approval record including decided-side fields. Used by
+/// the History tab so operators can review what they (or the
+/// system) decided.
+class ApprovalRecord {
+  final String id;
+  final String flowName;
+  final String stepId;
+  final String prompt;
+  final String? payloadPreview;
+  final DateTime createdAt;
+  final DateTime? expiresAt;
+  /// One of: pending / approved / rejected / expired.
+  final String status;
+  final DateTime? decidedAt;
+  /// Reviewer handle (e.g. "alice@studio") or "system" for
+  /// auto-expired approvals. Empty until decided.
+  final String decidedBy;
+  /// Reject reason — empty for approve / pending / expired.
+  final String reason;
+
+  const ApprovalRecord({
+    required this.id,
+    required this.flowName,
+    required this.stepId,
+    required this.prompt,
+    required this.payloadPreview,
+    required this.createdAt,
+    required this.expiresAt,
+    required this.status,
+    required this.decidedAt,
+    required this.decidedBy,
+    required this.reason,
+  });
+}
+
 class SystemAiStatus {
   final bool enabled;
   final String provider;