docs: fix session persistence wording & keep per-language version markers

[AmisKwok]

Summary / 摘要

Fix the Session Persistence description in the bilingual READMEs and keep the version-availability markers in each language. / 修正中英双版 README 中会话持久化的存储描述，并让版本可用标记各自成文、互不混排。

Changes / 变更

• Clarify that logs / network requests / errors are persisted into the inspector's own zero_inspector_kit.db database file (SQLite-backed disk ring buffer surfaced in the Database tab), not a generic local SQLite store. / 明确日志、网络请求与异常落盘到插件自有的 zero_inspector_kit.db 数据库文件（基于 SQLite 的磁盘环形缓冲，会出现在 Database 标签页），而非泛指本地 SQLite。
• Restore the availability markers — since v1.9.0 in README.md and v1.9.0 起可用 / （v1.9.0 起） in README_zh.md — in English-only / Chinese-only form (no more mixed Available since v1.9.0 / v1.9.0 起可用 callouts). / 恢复可用性标记：README.md 只保留英文 since v1.9.0，README_zh.md 只保留中文 v1.9.0 起可用 / （v1.9.0 起），去掉此前中英混排的提示块。

Context / 背景

The v1.9.0 docs originally described persistence as "a local SQLite ring buffer", which reads as a generic store; v1.9.0 actually ships its own zero_inspector_kit.db. Also, the availability markers were dropped entirely in an earlier edit and the bilingual callouts mixed English with Chinese in the same blockquote. / v1.9.0 文档原先将持久化描述为"本地 SQLite 环形缓冲"，易被理解为通用存储；实际 v1.9.0 自带 zero_inspector_kit.db。此外此前编辑误删了可用性标记，且提示块中英混排。

Checklist / 检查项

• Title follows Conventional Commits / 标题符合约定式提交
• CI checks pass after merge / 合入后 CI 通过

Test plan

• Visually confirm README.md contains no Chinese version markers and README_zh.md contains no English "Available since …"; check the Session Persistence / Error Monitor / Memory Monitor sections show their markers in the correct single language and reference zero_inspector_kit.db. / 目检 README.md 无中文版本标记、README_zh.md 无 "Available since …"；确认会话持久化 / 异常监控 / 内存监控小节各自的版本标记为单一语言且指向 zero_inspector_kit.db。

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