feat(adapters): add Codex Gateway adapter

[Ricky-7-Yan]

Description | 描述

Adds a lightweight Codex/CLI Gateway adapter and a platform adapter guide. The adapter maps Codex-like agent lifecycle events to the existing TDAI Gateway endpoints while keeping memory logic inside TdaiCore.

Related Issue | 关联 Issue

Closes #235

Change Type | 修改类型

• New platform adapter
• Documentation
• Tests added

Self-test Checklist | 自测清单

• Reviewed TdaiCore recall/capture/search boundaries
• Compared in-process OpenClaw adapter with Hermes/Gateway sidecar flow
• Added CodexMemoryAdapter for Gateway-backed recall, capture, search, and session flush
• Exported the adapter from src/adapters
• Added platform adapter guide and best practices
• Added unit coverage for auth headers, capture payloads, and Gateway errors

Verification | 验证

• npx.cmd vitest run src/adapters/codex/gateway-client.test.ts
• npm.cmd run build
• git diff --check

[Maxwell-Code07]

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