v0.1.3 — fetch retries + working auto re-check

Fixed

• fetch 自动重试 (Fetch retries). /check、/preview、/update 中的 git fetch --tags 现在自动重试 3 次（间隔 5 秒）。之前单次网络抖动（如 SSL 连接被重置）就会让整次检查失败，页面持续显示过期的版本信息。
  The git fetch in /check, /preview and /update now retries automatically (3 attempts, 5 s apart). A single network hiccup no longer poisons the whole check and leaves the page showing a stale version.

• 自动重查真正生效 (The auto re-check actually works now). 客户端自动检查的陈旧阈值从 12 小时缩短到 30 分钟，并把「每个会话只自动检查一次」的守卫改为 30 分钟限频——页面保持打开时版本数据不会陈旧超过约 30 分钟，上游发布新版本后页面会自动发现。
  The client auto-check staleness threshold drops from 12 h to 30 min, and the once-per-session guard becomes a 30-min rate limit — while the page stays open, version data can never be older than about 30 minutes, so a new upstream release surfaces on its own.

Added

• 数据陈旧提示 (Staleness hints). 「上次检查」现在附带相对时间（如「5 分钟前」）；缓存超过 30 分钟时时间戳变为琥珀色，并出现软提示引导点击「检查更新」。
  "Last checked" now shows a relative age; when the cache is older than 30 minutes the timestamp turns amber and a soft note prompts a re-check.