feat(sessions): show calendar dates with relative time and enable dat…

[rhine9473]

Summary

This PR improves the session timestamp presentation and searchability in /sessions:

1. Consistent Structure: Replaces ragged and inconsistent relative words (e.g. Yesterday vs 3d ago) with a unified two-part format:
   • Today's sessions: HH:MM (Xm/Xh ago) (e.g. 14:30 (2h ago))
   • Past sessions: MM-DD (Xd ago) (e.g. 09-06 (12d ago)), or YYYY-MM across years.
   • The primary time column (HH:MM and MM-DD) maintains a strictly aligned 5-character width.
2. Date Searchability: Includes formatted date and relative time strings into buildSearchText, allowing users to filter sessions by year, month, or calendar date (e.g.
   typing 2026 or 09-).
3. Unit Tests: Adds test coverage under tests/extensions/sessions/sessions.test.ts.

Testing

• node --test --experimental-strip-types tests/extensions/sessions/*.test.ts (11 passed, 0 failed)
• Verified locally in interactive TUI on Windows.
• Biome check verified clean.

[tt-a1i]

审查提交：f0fdbee361a7b4bb76adc4dd31aeb26e0bbde22f。

需要修改后再合并。

具体问题

P2 — 依赖真实时钟的日期测试每天凌晨必然失败 · tests/extensions/sessions/sessions.test.ts:151

Freeze Asia/Shanghai clock at 2026-09-21 00:05: test expects HH:mm (10m ago), gets 09-20 (0d ago). 6 pass / 1 fail. Also cross-year assumptions affect January.

验证范围

Complete two-file diff reviewed; deterministic frozen-clock reproduction saved in test-midnight.log.

限制与后续

No real TUI acceptance; yesterday 0d label is an additional UX ambiguity, not separately escalated.

[tt-a1i]

复审提交 8112d6e6b872c499c9debcd185488876217c6358。

此前的确定性问题已修复：格式化函数接收显式时钟，测试固定了普通、跨午夜和跨年边界，不再依赖运行时当天日期。当前所有远端检查通过，未发现新的阻断问题。

当前语义按经过时长划分：不足 24 小时即使跨过午夜仍显示 HH:mm，而不是按日历日立即切为 MM-DD。这是当前实现和新增断言明确选择的行为；如果产品要求“昨天一律显示日期”，需要另行调整，但不再是测试偶发问题。未执行真实 TUI 目视验收。