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/i18n/en.json

@@ -26,7 +26,6 @@
     "garage": "Garage",
     "charging": "Charging",
     "settings": "Settings",
-    "users": "Users",
     "lightMode": "Light mode",
     "darkMode": "Dark mode",
     "signedIn": "Signed in",
@@ -122,15 +121,15 @@
   },
 
   "admin": {
-    "eyebrow": "Admin",
     "title": "Users",
     "subtitleAll": "Accounts across every organization.",
     "subtitleOrg": "Accounts in your organization.",
-    "subtitleOrgsNote": "Organizations are managed in Settings.",
     "addUser": "Add user",
     "colEmail": "Email",
     "colName": "Name",
     "colOrganization": "Organization",
+    "noOrganization": "— No organization —",
+    "organizationHint": "Leave unset to create an account that belongs to no organization.",
     "colRole": "Role",
     "colCreated": "Created",
     "you": "(you)",
@@ -162,7 +161,9 @@
     "subtitle": "Manage your account, appearance, and data.",
     "tabs": {
       "personal": "Personal settings",
-      "integrations": "Integrations"
+      "integrations": "Integrations",
+      "users": "Users",
+      "organization": "Organization"
     },
 
     "account": {