docs: plan the narrow pages' heading alignment

Settings and the user form leave their heading at the left of the reading
measure while the card floats 12rem to the right of it. main > * caps every
child at 48rem and centres it; .card.narrow overrides the max-width down to
24rem but not the auto margins it never mentions, so the two centre on
different measures and half the difference is the offset.

Records what the question was actually about: not what is wrong with Settings
but what it shares with exactly one other page. Four templates use the narrow
card and eleven use a full-width one, which sorts every page into three groups
— full-width card, narrow card without navigation, narrow card with it — and
only the last has the problem. Settings and the user form are the only pages
that are both signed-in and built from a single narrow card; every other page
has one of those properties, never both.

Also records why the obvious fix is unavailable, so it is not tried a fourth
time: the shell centres the navigation and the page as a pair, so anything that
changes the column width is visible from the navigation (296px, measured). The
fix has to work inside the column.

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

docs/roadmap.md

@@ -30,6 +30,7 @@ in `git log` and [CHANGELOG.md](../CHANGELOG.md).
 | contributing | `CONTRIBUTING.md` | candidate | — |
 | dmarc-reports | DMARC aggregate report ingestion and panel UI | candidate | [plans/dmarc-reports.md](plans/dmarc-reports.md) |
 | logrotate-mode | `mail.log` stops rotating in some builds | candidate | [plans/logrotate-mode.md](plans/logrotate-mode.md) |
+| narrow-page-alignment | Settings and the user form: heading and card do not share an edge | candidate | [plans/narrow-page-alignment.md](plans/narrow-page-alignment.md) |
 
 **Recommended order** (not binding): **inbound-relay** first among agreed
 items — it is the largest remaining 1.x+ extension. Candidates need explicit