Add adjustable context size, custom chatbot name, and cat icon for AI chat

Settings > AI tab now includes context size slider (2048–131072) with VRAM
estimate and a chatbot name field. ChatService reads both dynamically instead
of hardcoding num_ctx=16384 and "Purrse AI". Chat panel FAB and empty state
use mdi-cat icon to match the rest of the app.

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

src/Purrse.Api/Services/ChatService.cs

@@ -113,6 +113,8 @@ public class ChatService : IChatService
         var settings = await _db.AiCategorizationSettings.FirstOrDefaultAsync(s => s.UserId == userId);
         var ollamaUrl = settings?.OllamaUrl ?? "http://localhost:11434";
         var modelName = settings?.ModelName ?? "llama3.1:8b";
+        var chatContextSize = settings?.ChatContextSize ?? 16384;
+        var chatBotName = settings?.ChatBotName;
 
         // Save user message
         var userMessage = new ChatMessage
@@ -130,10 +132,15 @@ public class ChatService : IChatService
         var ollamaMessages = new List<OllamaToolMessage>();
 
         // System prompt
+        var systemPrompt = string.Format(SystemPromptTemplate, DateTime.UtcNow.ToString("yyyy-MM-dd"));
+        if (!string.IsNullOrWhiteSpace(chatBotName))
+        {
+            systemPrompt += $"\nYour name is {chatBotName}.";
+        }
         ollamaMessages.Add(new OllamaToolMessage
         {
             Role = "system",
-            Content = string.Format(SystemPromptTemplate, DateTime.UtcNow.ToString("yyyy-MM-dd"))
+            Content = systemPrompt
         });
 
         // Last 20 conversation messages
@@ -199,7 +206,7 @@ public class ChatService : IChatService
                 Messages = ollamaMessages,
                 Stream = false,
                 Tools = tools,
-                Options = new OllamaRequestOptions { NumCtx = 16384 }
+                Options = new OllamaRequestOptions { NumCtx = chatContextSize }
             };
 
             var response = await CallOllamaAsync(ollamaUrl, ollamaRequest);
@@ -272,7 +279,7 @@ public class ChatService : IChatService
                         Messages = ollamaMessages,
                         Stream = false,
                         Tools = null, // drop tools so the model focuses on the page data
-                        Options = new OllamaRequestOptions { NumCtx = 16384 }
+                        Options = new OllamaRequestOptions { NumCtx = chatContextSize }
                     };
                     var retryResponse = await CallOllamaAsync(ollamaUrl, retryRequest);
                     rawContent = retryResponse?.Message?.Content;