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>

motia-backend/streams/taskLog.ts

@@ -0,0 +1,62 @@
+/**
+ * TaskLog Stream Definition
+ *
+ * Manages log entries for each task execution.
+ * Uses sessionId as groupId for per-task log isolation.
+ * Retains recent N entries for state recovery.
+ *
+ * @see Requirements 4.2, 4.6
+ */
+
+import { defineStream } from '@motia/core'
+import { z } from 'zod'
+import type { StepId } from './taskState'
+
+// Log level enum
+export const LogLevelSchema = z.enum(['INFO', 'WARN', 'ERROR'])
+export type LogLevel = z.infer<typeof LogLevelSchema>
+
+// Task log entry schema
+export const TaskLogEntrySchema = z.object({
+  sessionId: z.string(),
+  stepId: z.string(), // StepId type
+  ts: z.string(), // ISO timestamp
+  level: LogLevelSchema,
+  message: z.string(),
+  seq: z.number(), // Log sequence number for ordering
+})
+export type TaskLogEntry = z.infer<typeof TaskLogEntrySchema>
+
+// Maximum number of log entries to retain per task
+export const MAX_LOG_ENTRIES = 1000
+
+/**
+ * Create a new log entry
+ */
+export function createLogEntry(
+  sessionId: string,
+  stepId: StepId,
+  level: LogLevel,
+  message: string,
+  seq: number
+): TaskLogEntry {
+  return {
+    sessionId,
+    stepId,
+    ts: new Date().toISOString(),
+    level,
+    message,
+    seq,
+  }
+}
+
+// Define the taskLog stream
+export const taskLogStream = defineStream({
+  name: 'taskLog',
+  schema: TaskLogEntrySchema,
+  persistence: {
+    enabled: true,
+    // Retain recent entries for state recovery
+    maxEntries: MAX_LOG_ENTRIES,
+  },
+})