feat(studio): clear-audit-log button on Audit page (v0.15.0)

Operators can now clear dev-noise from the audit log without
dropping to the CLI. Top-bar broom icon next to the filter
chips opens a two-field dialog (reviewer pre-filled from $USER,
reason required). On submit the hub call returns the purged
count + active channel; both are shown back in a snackbar.

Compliance-locked channels (beta/production) are refused
server-side; the dialog surfaces the rejection reason via a
friendly error message instead of the raw gRPC status string.

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

lib/data/hub.dart

@@ -270,6 +270,23 @@ class HubService {
     );
   }
 
+  /// Wipe the audit log on the active channel and seed a fresh
+  /// `chain.reset` marker. Refused server-side on `beta` /
+  /// `production`; the gRPC error surfaces as an exception so
+  /// the caller can show the operator why it was blocked.
+  /// Returns `(purged, channel)` so the UI can confirm what
+  /// just happened.
+  Future<({int purged, String channel})> clearEventLog({
+    required String reviewer,
+    required String reason,
+  }) async {
+    final r = await _client.clearEventLog(
+      reviewer: reviewer,
+      reason: reason,
+    );
+    return (purged: r.purged.toInt(), channel: r.channel);
+  }
+
   /// Active channel + per-channel daemon status snapshot.
   Future<ChannelStatusSnapshot> channelStatus() async {
     final r = await _client.channelStatus();