fix: k8s on-premise deployment and session persistence

Database fixes:
- Add hostPath.type=DirectoryOrCreate so kubelet auto-creates /mnt/data/mysql
- Add fsGroup=999 so MySQL process can write to the hostPath volume
- Add MYSQL_ROOT_HOST=% to allow backend pods to authenticate as root
- Fix liveness/readiness probes to include credentials (-p$MYSQL_ROOT_PASSWORD)
- Increase probe initialDelaySeconds (30/60s) for slow first-run init
- Add 15s grace sleep in backend initContainer after MySQL TCP is up
- Add persistentVolumeReclaimPolicy=Retain to prevent accidental data loss
- Explicit accessModes+resources in PVC patch to avoid list merge ambiguity
- Add nodeAffinity comment in PV for multi-node cluster guidance

Ingress/nginx fixes:
- Remove broken rewrite-target=/ that was rewriting all paths (incl /api) to /
- Route /socket.io directly to backend for WebSocket support
- Add /socket.io/ proxy location to both nginx.conf and K8s ConfigMap

Frontend fix:
- Persist currentUser to localStorage on login so page refresh no longer
  clears session and redirects users back to the login page

Tooling:
- Add k8s/overlays/on-premise/deploy.sh for one-command deployment

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

src/App.tsx

@@ -25,7 +25,10 @@ const VIEW_PAGES = ['calendar', 'kanban', 'list'];
 
 export default function App() {
   const now = new Date();
-  const [currentUser, setCurrentUser] = useState<User | null>(null);
+  const [currentUser, setCurrentUser] = useState<User | null>(() => {
+    try { const s = localStorage.getItem('currentUser'); return s ? JSON.parse(s) : null; }
+    catch { return null; }
+  });
   const [users, setUsers] = useState<User[]>([]);
   const [tasks, setTasks] = useState<Task[]>([]);
   const [activePage, setActivePage] = useState('calendar');
@@ -58,7 +61,7 @@ export default function App() {
       .finally(() => setLoading(false));
   }, [currentUser]);
 
-  if (!currentUser) return <LoginPage onLogin={u => { setCurrentUser(u); setActivePage('calendar'); setActiveView('calendar'); }} />;
+  if (!currentUser) return <LoginPage onLogin={u => { localStorage.setItem('currentUser', JSON.stringify(u)); setCurrentUser(u); setActivePage('calendar'); setActiveView('calendar'); }} />;
 
   const handleNavigate = (page: string) => {
     setActivePage(page);
@@ -250,7 +253,7 @@ export default function App() {
           onOpenSidebar={() => setSidebarOpen(true)} users={users} />
         <div className="app-body">
           <Sidebar currentUser={currentUser} activePage={activePage} onNavigate={handleNavigate}
-            onSignOut={() => { setCurrentUser(null); setActivePage('calendar'); setActiveView('calendar'); setSidebarOpen(false); }}
+            onSignOut={() => { localStorage.removeItem('currentUser'); setCurrentUser(null); setActivePage('calendar'); setActiveView('calendar'); setSidebarOpen(false); }}
             isOpen={sidebarOpen} onClose={() => setSidebarOpen(false)} users={users} />
           <div className="main-content">
             {displayPage === 'calendar' && (