feat(planning): warn of an overrun only past the displayed range

The expected wait sits near the middle of recent waits, so about half of
all runs pass it. Between the expected wait and the top of the range
shown before Calculate, the percentage now holds at 95% with no
remaining-time line; "Taking longer than expected" appears and is
announced only past that top.

Refs #300

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/planning-duration.md

@@ -96,10 +96,13 @@ cannot move it backwards. On Cancel, the tick stops and the percentage freezes.
 Below the status, one line names the current planning stage. For an
 optimization or preference stage, it shows the rule's name. When `e` is at least
 3 seconds, a second line shows "About N s left". This is in whole seconds under
-10 seconds, 5-second steps under a minute and whole minutes after that. Once
-the elapsed time reaches `e`, the line reads "Taking longer than expected" for
-any `e`, and the live status announces it once. Both lines are visible text,
-not live regions, and are hidden after Cancel.
+10 seconds, 5-second steps under a minute and whole minutes after that. From
+`e` to the top of the range shown before Calculate, the percentage holds at 95%
+and that line is hidden. Because `e` sits near the middle of recent waits, about
+half of all runs pass it, so it is no reason to warn the user. Past the top of
+the range, for any `e`, the line reads "Taking longer than expected" and the
+live status announces it once. Both lines are visible text, not live regions,
+and are hidden after Cancel.
 
 ## What is timed