perf: cap the History list and fold column widths incrementally

History was appended to on every recorded run and never trimmed, and every
event re-sorted the whole slice and re-measured the Job, Detail and Log
columns across every row. The per-run cost therefore grew with the number of
rows, in exactly the mode the app is designed for: left in the tray for days.

The session History now keeps the newest maxHistoryRows (1000) records, the
way maxJobLogs caps a job's own activity list, and drops the oldest from the
front, zeroing the tail so a dropped record's full captured output is not
kept alive by the backing array. Column widths move into a historyLog value
that folds each new record into the current maxima instead of rescanning.
Widths only grow within a theme, so a column never narrows when a record ages
out; a theme change is the one case that still rescans, because every stored
width was measured at the old text size.

Measured with a throwaway benchmark over 5000 accumulated records: one
refresh went from 15.8 ms to 0.9 ms. At the new cap the full width rescan
alone costs 1.5 ms, so both halves of the fix carry weight.

Plan item 6 of docs/PROJECT_REVIEW_PLAN.md (finding 3.1).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/CHANGELOG.md

@@ -39,6 +39,13 @@ the app icon (experimental).**
   longer than its own interval no longer accumulates an unbounded backlog that
   then runs back-to-back indefinitely. The job details pane now shows the
   queued-run count (", N queued") whenever it is non-zero.
+- The History tab no longer grows without bound: it keeps the newest 1000
+  records and drops the oldest, the way a job's own activity list is capped.
+  Column widths are also folded in one record at a time instead of being
+  re-measured across every row on every event, so recording a run no longer
+  gets slower the longer the app has been running. Measured on 5000 accumulated
+  records, one History redraw went from **15.8 ms to 0.9 ms**; at the new cap
+  the width rescan alone accounted for 1.5 ms of every redraw.
 
 **Jobs:**