The DesktopSidebar previously had no entry point for /collective/manage,
making member-management and the new common-items / tags subsections
unreachable from the chrome on desktop. The MobileDrawer already linked
it from inside the collective switcher block; desktop didn't.
- Adds a `<div aria-hidden>` divider with `my-2 border-t` to separate
the section nav (lists / tasks / notes / search) from the manage
entry.
- Adds a `Users`-iconed link to `/collective/manage` as the last nav
item, with the same active-state styling as the other entries.
- Not gated by `$enabledSections` (membership management is orthogonal
to feature toggles — same call as the Admin entry in the footer).
- Reuses the existing `m.manage_title()` Paraglide string; no new
strings.
Tests: tests/e2e/sidebar-manage-link.test.ts adds SBM-01 (link visible
and navigates) + SBM-02 (divider present in <nav>).
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
