refactor(pill-nav): drop Settings entry, guard on settingsHref

Settings lives in the Workbench now — no longer needs its own pill.
settingsHref becomes optional; both places that render the entry
(user-menu link list + nav overflow dropdown) skip it when unset.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/mana/apps/web/src/routes/(app)/+layout.svelte

@@ -974,7 +974,6 @@
 					currentSyncLabel={syncStatus.label}
 					{appItems}
 					{userEmail}
-					settingsHref="/"
 					manaHref="/mana"
 					profileHref="/profile"
 					spiralHref="/spiral"