Settings: fold Users and Organization into the Settings tabs

The left rail is back to the three places you actually go — Garage,
Charging, Settings — and user management moves inside Settings as an
admin-only tab, next to a new Organization tab that used to be a card
buried in the personal settings. Tab order is Personal settings, Users,
Organization, Integrations. /admin redirects to /settings?tab=users so
old links keep working, and ?tab= picks the starting tab in general.

AdminUsers moves from views/ to components/ since it is a panel now, not
a route, and its page header becomes a section header like its
neighbours. The personal panel was split in two around the integrations
markup, which left no gap between the Profile and Privacy cards; it is
one block again.

Creating a user gets an organization picker for superadmins, defaulting
to "no organization" so an org-less account stays a deliberate choice.
Admins see no picker: the server pins their members to their own org
regardless, which users_test.go now covers along with both superadmin
paths.

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

Web App/web/src/auth.js

@@ -17,7 +17,7 @@ export const isAuthenticated = computed(() => !!state.token);
 
 // Roles that may manage users. A superadmin is an admin that also spans every
 // organization; the API Server enforces the difference, the UI just needs to
-// know whether to offer the Users screen at all.
+// know whether to offer the Settings › Users tab at all.
 const MANAGER_ROLES = ["admin", "superadmin"];
 
 // Admin gate for the UI. Driven by the full profile (fetched from /api/me),