chore: 初始版本提交 - 简化架构 + 轮询改造

- 移除 Motia Streams 实时通信，改用 3 秒轮询
- 简化前端代码，移除冗余组件
- 简化后端架构，准备 FastAPI 重构
- 更新 pixi.toml 环境配置
- 保留 bttoxin_digger_v5_repro 作为参考文档

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

docker/scripts/entrypoint.backend.sh

@@ -0,0 +1,24 @@
+#!/bin/bash
+# Backend-only entrypoint for Traefik deployment
+# Nginx is handled by separate frontend container
+
+set -e
+
+# Create jobs directory
+mkdir -p /app/jobs
+
+# Activate pixi webbackend environment
+echo "Activating pixi webbackend environment..."
+pixi shell-hook -e webbackend > /app/activate.sh
+echo 'exec "$@"' >> /app/activate.sh
+
+# Start backend
+echo "Starting BtToxin Pipeline backend..."
+exec /bin/bash /app/activate.sh bash -c "
+    mkdir -p /app/jobs
+
+    # Set API_BASE_URL from environment or default
+    export API_BASE_URL=\${API_BASE_URL:-http://localhost}
+
+    uvicorn web.backend.main:app --host 0.0.0.0 --port 8000
+"