feat: Auto-Context im Frontend anzeigen und in DB persistieren

- recalled_context-Header verstärkt (klare Nutzungs-Anweisung statt passivem Hinweis)
- SSE-Event 'auto_context' ans Frontend senden für Live-Anzeige
- Auto-Context als Message (type=auto_context) in DB speichern
- Aufklappbare Auto-Context-Box im Chat-Stream und History-Rendering

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Services/AnthropicService.Streaming.cs

@@ -64,7 +64,17 @@ public partial class AnthropicService
                 {
                     var autoCtx = await BuildAutoContextAsync(messages, chainId, agentId);
                     if (autoCtx != null)
+                    {
                         systemPrompt.Add(new { type = "text", text = autoCtx });
+                        await SseHelper.TryWriteSse(response, "auto_context", new { context = autoCtx }, sseCt);
+                        await _db.SaveMessage(new MessageRecord
+                        {
+                            ChainId = chainId,
+                            Role = "system",
+                            Type = "auto_context",
+                            Content = autoCtx
+                        });
+                    }
                 }
                 catch (Exception ex)
                 {