Add floating AI chat panel with page context awareness

Replace the standalone /chat page with a bottom-right floating widget
available on every page. The panel sends page context with each message
so the AI knows what the user is viewing. On the Transactions page,
the full visible transaction list (with filters) is serialized into
the context so the AI can answer questions about on-screen entries.

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

src/Purrse.Api/Services/ChatService.cs

@@ -134,6 +134,16 @@ public class ChatService : IChatService
             Content = string.Format(SystemPromptTemplate, DateTime.UtcNow.ToString("yyyy-MM-dd"))
         });
 
+        // Page context
+        if (!string.IsNullOrEmpty(request.PageContext))
+        {
+            ollamaMessages.Add(new OllamaToolMessage
+            {
+                Role = "system",
+                Content = $"The user is currently viewing: {request.PageContext}"
+            });
+        }
+
         // Last 20 conversation messages
         var recentMessages = conversation.Messages
             .OrderBy(m => m.CreatedAt)

src/Purrse.Core/DTOs/ChatDtos.cs

@@ -3,7 +3,7 @@ using System.Text.Json.Serialization;
 namespace Purrse.Core.DTOs;
 
 // API DTOs
-public record SendChatMessageRequest(Guid? ConversationId, string Message);
+public record SendChatMessageRequest(Guid? ConversationId, string Message, string? PageContext = null);
 
 public record SendChatMessageResponse(Guid ConversationId, ChatMessageResponse AssistantMessage);