fix(events, docs): mark ended events, recover offline, align summaries

[m1ngsama]

The second audit found the heatmap's hierarchy inverted, ended events unmarked in week and month lists, dead-end offline errors, and docs summaries cut at 44 characters or wrapping.

• Docs summaries sit in one column that fills the width and clips with "…"; the docs hub shows "下方还有 N 项" when items are hidden.
• The heatmap fades empty days and uses one green ramp for activity; month labels never touch or disappear, falling back to month numbers when full names don't fit. "近一年活跃度" appears only when the hub has no room for the heatmap.
• 本周 / 本月 dim ended events and mark them "已结束"; event detail shows the time range.
• While showing cached data the offline notice appears on every events screen. With nothing cached, events and docs say the network looks down, show a hint, and offer 重试.
• Docs sections show a dim "…" for titles not yet loaded and fill them in place; search results are titled with the query and count, show progress ("已检索 n / N 篇"), and no longer repeat titles in excerpts.
• The reader shows link text only; f lists external links with their address and opens them. Lines never end on “ or start on ”; input footers read "⏎ 确认 · Esc 返回 · Ctrl+C 退出".
• The next-event banner uses ● like the next-class banner, so neither looks selected.