Add admin enhancements: impersonation, plan management, org status enforcement

Enhancement 1 - Block suspended/archived org access:
- Add org status check in switchOrganization() (auth.service.ts)
- Filter suspended/archived orgs from login response (generateTokenResponse)
- Add org status guard with 60s cache in TenantMiddleware
- Frontend: filter orgs in SelectOrgPage, add 403 handler in api.ts

Enhancement 2 - Change tenant plan level:
- Add updatePlanLevel() to organizations.service.ts
- Add PUT /admin/organizations/:id/plan endpoint
- Frontend: clickable plan dropdown in Organizations table + confirmation modal
- Plan level Select in tenant detail drawer

Enhancement 3 - User impersonation:
- Add impersonateUser() to auth.service.ts with impersonatedBy JWT claim
- Add POST /admin/impersonate/:userId endpoint
- Frontend: Impersonate button in Users tab (disabled for admins)
- Impersonation state management in authStore (start/stop/persist)
- Orange impersonation banner in AppLayout header with stop button

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/components/layout/AppLayout.tsx

@@ -1,4 +1,4 @@
-import { AppShell, Burger, Group, Text, Menu, UnstyledButton, Avatar } from '@mantine/core';
+import { AppShell, Burger, Group, Text, Menu, UnstyledButton, Avatar, Alert, Button } from '@mantine/core';
 import { useDisclosure } from '@mantine/hooks';
 import {
   IconLogout,
@@ -7,6 +7,7 @@ import {
   IconSettings,
   IconUserCog,
   IconUsersGroup,
+  IconEyeOff,
 } from '@tabler/icons-react';
 import { Outlet, useNavigate } from 'react-router-dom';
 import { useAuthStore } from '../../stores/authStore';
@@ -15,25 +16,53 @@ import logoSrc from '../../assets/logo.svg';
 
 export function AppLayout() {
   const [opened, { toggle, close }] = useDisclosure();
-  const { user, currentOrg, logout } = useAuthStore();
+  const { user, currentOrg, logout, impersonationOriginal, stopImpersonation } = useAuthStore();
   const navigate = useNavigate();
+  const isImpersonating = !!impersonationOriginal;
 
   const handleLogout = () => {
     logout();
     navigate('/login');
   };
 
+  const handleStopImpersonation = () => {
+    stopImpersonation();
+    navigate('/admin');
+  };
+
   // Tenant admins (president role) can manage org members
   const isTenantAdmin = currentOrg?.role === 'president' || currentOrg?.role === 'admin';
 
   return (
     <AppShell
-      header={{ height: 60 }}
+      header={{ height: isImpersonating ? 100 : 60 }}
       navbar={{ width: 260, breakpoint: 'sm', collapsed: { mobile: !opened } }}
       padding="md"
     >
       <AppShell.Header>
-        <Group h="100%" px="md" justify="space-between">
+        {isImpersonating && (
+          <Group
+            h={40}
+            px="md"
+            justify="center"
+            gap="xs"
+            style={{ backgroundColor: 'var(--mantine-color-orange-6)' }}
+          >
+            <Text size="sm" fw={600} c="white">
+              Impersonating {user?.firstName} {user?.lastName} ({user?.email})
+            </Text>
+            <Button
+              size="xs"
+              variant="white"
+              color="orange"
+              leftSection={<IconEyeOff size={14} />}
+              onClick={handleStopImpersonation}
+            >
+              Stop Impersonating
+            </Button>
+          </Group>
+        )}
+        <Group h={60} px="md" justify="space-between">
           <Group>
             <Burger opened={opened} onClick={toggle} hiddenFrom="sm" size="sm" />
             <img src={logoSrc} alt="HOA LedgerIQ" style={{ height: 40 }} />
@@ -46,7 +75,7 @@ export function AppLayout() {
               <Menu.Target>
                 <UnstyledButton>
                   <Group gap="xs">
-                    <Avatar size="sm" radius="xl" color="blue">
+                    <Avatar size="sm" radius="xl" color={isImpersonating ? 'orange' : 'blue'}>
                       {user?.firstName?.[0]}{user?.lastName?.[0]}
                     </Avatar>
                     <Text size="sm">{user?.firstName} {user?.lastName}</Text>
@@ -55,6 +84,18 @@ export function AppLayout() {
                 </UnstyledButton>
               </Menu.Target>
               <Menu.Dropdown>
+                {isImpersonating && (
+                  <>
+                    <Menu.Item
+                      color="orange"
+                      leftSection={<IconEyeOff size={14} />}
+                      onClick={handleStopImpersonation}
+                    >
+                      Stop Impersonating
+                    </Menu.Item>
+                    <Menu.Divider />
+                  </>
+                )}
                 <Menu.Label>Account</Menu.Label>
                 <Menu.Item
                   leftSection={<IconUserCog size={14} />}