Add landing page, redesign emails, and return updated task on completion

- Integrate landing page into Go app (served at root /)
- Add STATIC_DIR config for static file serving
- Redesign all email templates with modern dark theme styling
- Add app icon to email headers
- Return updated task with kanban_column in completion response
- Update task DTO to include kanban column for client-side state updates

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

internal/services/task_service.go

@@ -501,10 +501,20 @@ func (s *TaskService) CreateCompletion(req *requests.CreateTaskCompletionRequest
 		return nil, err
 	}
 
+	// Reload task with updated completions (so client can update kanban column)
+	task, err = s.taskRepo.FindByID(req.TaskID)
+	if err != nil {
+		// Non-fatal - still return the completion, just without the task
+		log.Warn().Err(err).Uint("task_id", req.TaskID).Msg("Failed to reload task after completion")
+		resp := responses.NewTaskCompletionResponse(completion)
+		return &resp, nil
+	}
+
 	// Send notification to residence owner and other users
 	s.sendTaskCompletedNotification(task, completion)
 
-	resp := responses.NewTaskCompletionResponse(completion)
+	// Return completion with updated task (includes kanban_column for UI update)
+	resp := responses.NewTaskCompletionWithTaskResponse(completion, task, 30)
 	return &resp, nil
 }