Show per-member token usage badges on panel bubbles

memberUsage was already populated for CLI members (from the result event)
and Anthropic-API members (via the tool loop), but it was never written to
the panel_member_done SSE event or the persisted content JSON, so the
frontend had no token data to render.

Add the token fields (input/output/cacheRead/cacheCreation) to both the
SSE event and the persisted JSON, and render them via a shared
buildPanelMemberMeta helper used by both the live stream and history, so
the badge survives F5. OpenAI members (no per-turn tokens), error members,
and pre-existing history without token fields fall through to no badge.

The badge is display-only; aggregation into the worker/chain total via
seedUsage is unchanged, so there is no double counting and no DB migration.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Services/AnthropicService.Panel.cs

@@ -245,7 +245,15 @@ public partial class AnthropicService
         }
         if (segments.Count > 0)
         {
-            var content = JsonSerializer.Serialize(new { name, model = member.ModelId, layer, totalLayers, segments });
+            var content = JsonSerializer.Serialize(new
+            {
+                name, model = member.ModelId, layer, totalLayers,
+                inputTokens = memberUsage?.InputTokens ?? 0,
+                outputTokens = memberUsage?.OutputTokens ?? 0,
+                cacheReadTokens = memberUsage?.CacheReadTokens ?? 0,
+                cacheCreationTokens = memberUsage?.CacheCreationTokens ?? 0,
+                segments
+            });
             await _db.SaveMessage(new MessageRecord
             {
                 ChainId = chainId, Iteration = layer * 100 + index + 1,
@@ -255,7 +263,14 @@ public partial class AnthropicService
         }
 
         await SseHelper.TryWriteSse(response, "panel_member_done",
-            new { index, name, model = member.ModelId, text }, sseCt, sseGate);
+            new
+            {
+                index, name, model = member.ModelId, text,
+                inputTokens = memberUsage?.InputTokens ?? 0,
+                outputTokens = memberUsage?.OutputTokens ?? 0,
+                cacheReadTokens = memberUsage?.CacheReadTokens ?? 0,
+                cacheCreationTokens = memberUsage?.CacheCreationTokens ?? 0
+            }, sseCt, sseGate);
 
         return new PanelMemberResult { Index = index, Name = name, Model = member.ModelId, Text = text, Usage = memberUsage };
     }