fix(tools): count important commits against the changelog fold limit

The fold limit only sliced normal commits, so important commits rendered
above the fold without consuming any of the budget. A section with 4
important commits and a limit of 5 showed all 5 normal commits too (9
total) and never emitted the Show all details block.

Subtract the important count from the limit so it caps total above-fold
items, clamped at 0 so important commits are still never collapsed when
they alone meet or exceed the limit.

Author: vagabondHustler

tools/changelog_template.md.j2

@@ -42,8 +42,9 @@
 {% else %}
 {% set important = sections[change_key] | selectattr("important") | list %}
 {% set normal = sections[change_key] | rejectattr("important") | list %}
-{% set above_fold = normal[:fold_limit] %}
-{% set collapsed = normal[fold_limit:] %}
+{% set normal_slots = [fold_limit - (important | length), 0] | max %}
+{% set above_fold = normal[:normal_slots] %}
+{% set collapsed = normal[normal_slots:] %}
 {% for change in important %}{{ render_commit(change) }}{% endfor %}
 {% for change in above_fold %}{{ render_commit(change) }}{% endfor %}
 {% if collapsed %}