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>

activate_backend.sh

@@ -0,0 +1,32 @@
+export PATH="/app/.pixi/envs/webbackend/bin:/root/.pixi/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
+export CONDA_SHLVL=1
+export CONDA_PREFIX=/app/.pixi/envs/webbackend
+export PIXI_PROJECT_NAME=bttoxin-pipeline
+export PIXI_PROJECT_ROOT=/app
+export PIXI_PROJECT_VERSION=0.1.0
+export PIXI_PROJECT_MANIFEST=/app/pixi.toml
+export PIXI_EXE=/usr/local/bin/pixi
+export PIXI_IN_SHELL=1
+export CONDA_DEFAULT_ENV=bttoxin-pipeline:webbackend
+export PIXI_ENVIRONMENT_NAME=webbackend
+export PIXI_ENVIRONMENT_PLATFORMS=linux-64
+export PIXI_PROMPT='(bttoxin-pipeline:webbackend) '
+
+# shellcheck shell=bash
+pixi() {
+    local first_arg="${1-}"
+
+    "${PIXI_EXE-}" "$@" || return $?
+
+    case "${first_arg-}" in
+    add | a | remove | rm | install | i)
+        eval "$("$PIXI_EXE" shell-hook --change-ps1 false)"
+        hash -r
+        ;;
+    esac || :
+
+    return 0
+}
+
+export PS1="(bttoxin-pipeline:webbackend) ${PS1:-}"
+exec uvicorn backend.app.main:app --reload --host 0.0.0.0 --port 8000 "$@"