Persist panel member token costs to DB via usage seed

Replace the separate panel_usage SSE event + frontend accumulator with
server-side seeding of the worker's usage object. Both the done-event and
FinalizeChain read from the same usage, so panel (Fusion/MoA) member tokens
now flow into the live badge AND the DB as a single source of truth — the
badge no longer drops to the worker-only value after F5.

- RunPanel takes a TokenUsage usageSink; accumulates member costs after the
  Task.WhenAll barrier (single-threaded, no lock)
- ChatEndpoint passes panelUsage as seedUsage to all three worker paths
- StreamChat / StreamChatViaCli / OpenAI StreamChat fold seedUsage into usage
  at creation time, so every exit path persists it
- OpenAI done-events extended with cacheCreation/cacheRead fields for live
  consistency when seeded by Anthropic members
- chat.js: remove redundant _panelUsage / _addPanelUsage / panel_usage
- TODO.md: mark the live-only v1 boundary closed, note the new mechanism

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

Services/AnthropicService.Cli.cs

@@ -38,6 +38,7 @@ public partial class AnthropicService
         string unityMcpToken = null,
         bool useAutoContext = true,
         string effort = null,
+        TokenUsage seedUsage = null,
         CancellationToken workCt = default,
         CancellationToken sseCt = default)
     {
@@ -50,6 +51,9 @@ public partial class AnthropicService
 
         var sw = System.Diagnostics.Stopwatch.StartNew();
         var usage = new TokenUsage();
+        // Panel-Member-Tokens (Fusion/MoA) vorab in die Chain-Usage falten → erscheinen im
+        // done-Event (Live-Badge) UND in FinalizeChain (DB, überlebt F5). Null/leer = No-op.
+        if (seedUsage != null) usage.Add(seedUsage);
         var fullText = new StringBuilder();
         var tempImagePaths = new List<string>();
         string mcpConfigPath = null;