Add Beryl Agent and harness source

agent-studio-mini/docs/architecture.md

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+# 架构
+
+```mermaid
+sequenceDiagram
+  participant U as assistant-ui
+  participant H as Fastify/Harness
+  participant P as Pi AgentSession
+  U->>H: POST message (202)
+  H->>P: prompt(text,{images})
+  P-->>H: session events
+  H-->>U: ordered SSE events
+  P->>H: save_report_draft
+  H-->>U: approval.required
+  U->>H: approve/deny
+  H-->>P: resume/block
+```
+
+`packages/shared` 是无 Node 依赖协议；`packages/harness` 是无 React/Fastify 的核心；Fastify 只组合协议；Web 的 Store reducer 按 sequence 投影消息、Run、Tool 与 Approval。