The account page's two error messages draw the shared danger callout, and .error-note leaves the stylesheet and §5d #7750

For: P0 Trust, specifically one design system with no page-local classes. Rewritten from #5074, which was parked as written. That issue said what to delete but not what to draw in its place.

Today .error-note is a page-local class: its rule is in src/web/style/components.ts:144, it is used at src/web/pages/account.ts:117 (notify URL form) and :854, and it is named in docs/design/sections/5d-page-local-classes.md.

Done looks like:

• [ ] Both messages in src/web/pages/account.ts draw an existing shared component in the danger tone: the one forms already use for a refused submit (look in src/web/ui.ts / src/web/flash.ts). Do not add a new class. The words stay the same and are still escaped.
• [ ] grep -rn error-note src docs finds nothing: the rule leaves components.ts and the name leaves §5d.
• [ ] A test posts an invalid notify URL to /settings/notify and sees the message in the shared component's markup. It fails without the change.
• [ ] bun scripts/design-lint.ts passes.

Files: src/web/pages/account.ts, src/web/style/components.ts, docs/design/sections/5d-page-local-classes.md, a test. Risks: the message must keep role/focus behaviour if the shared component has it; do not change the notify-URL validation.

Replaced by #7760: the same outcome, written fresh. This issue picked up a parked state from dropped #5218 when #5074 was split into it, so no builder could start it.