fix(tui): the /resume picker lists sessions that are more than 30 days old - #61

Summary

Plan decision 9. /resume left out every session that was last updated more than 30 days ago. The rule came from the upstream project. With the Python agent, a session that nobody touched for a month was gone from the picker, and only --resume <id> could still open it. The cutoff is removed. This is the tendency written in the plan: the agent pages the list, so a longer list is not a problem.

 parse_session_picker_entries(payload)
   for each row of payload.sessions
     skip a row with no usable first prompt or summary
-    skip a row whose updatedAt is older than now - 30 days
     skip a row whose updatedAt does not parse        # unchanged

Stacked on #60. The base of this PR is fix/tui-dead-settings-and-flags, because both PRs change CHANGELOG.md and scripts/tui_baseline.toml at the same lines. Merge #60 first. Then change the base of this PR to main if GitHub does not do it.

Evidence

• Before: picker_drops_old_conversation_past_cutoff_in_standard_acp_mode passes and asserts the drop: one row with updatedAt = 2020-01-01 gives an empty list. (Its failure message said the opposite.)
  After: two tests take its place. They assert what the old code dropped:

picker_keeps_a_session_older_than_30_days
  one row, updatedAt 2020-01-01                     -> 1 entry (id, summary, updated_at as given)
acp_session_list_page_keeps_old_and_new_sessions
  session/list page: s_new, s_old (2020), s_older (2019)
                                                    -> ids == [s_new, s_old, s_older], order kept

• pi-pager suite (scripts/tui_baseline.py test, nextest, Linux, WSL2): 5,657 passed, 0 failed, 12 skipped. Before: 5,656 (one test gone, two new). scripts/tui_baseline.toml goes up by the same one. CHANGELOG.md: one entry under ### Fixed.
• ruff check . and ruff format --check . pass on Windows. No Python file changes.

Merge Danger

Door: two-way. One revert brings the cutoff back.

Blast Radius: the list of the /resume picker. It can show more rows: a user with sessions from earlier months now sees them. The picker still reads up to 100 pages of 50 rows, and it still waits for all pages before it draws (about 0.8 s for 1,000 sessions on Windows; plan decision 11 is the open item that would draw while the pages arrive). --resume <id>, the agent, the session files and every other picker do not change. A row with no updatedAt that parses is still left out.