Add profile management (display name, email, password change, account deletion)

Full-stack profile section: DisplayName column on User model, profile CRUD
endpoints on AuthController, and complete Settings > Profile tab UI with
profile editing, password change, account info, and account deletion.

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

frontend/src/stores/auth.ts

@@ -7,6 +7,7 @@ export const useAuthStore = defineStore('auth', () => {
   const token = ref<string | null>(null)
   const refreshTokenValue = ref<string | null>(null)
   const username = ref<string | null>(null)
+  const displayName = ref<string | null>(null)
   const expiresAt = ref<string | null>(null)
 
   const isAuthenticated = computed(() => !!token.value)
@@ -15,6 +16,7 @@ export const useAuthStore = defineStore('auth', () => {
     token.value = localStorage.getItem('purrse_token')
     refreshTokenValue.value = localStorage.getItem('purrse_refresh_token')
     username.value = localStorage.getItem('purrse_username')
+    displayName.value = localStorage.getItem('purrse_display_name')
     expiresAt.value = localStorage.getItem('purrse_expires_at')
   }
 
@@ -22,10 +24,16 @@ export const useAuthStore = defineStore('auth', () => {
     token.value = auth.token
     refreshTokenValue.value = auth.refreshToken
     username.value = auth.username
+    displayName.value = auth.displayName
     expiresAt.value = auth.expiresAt
     localStorage.setItem('purrse_token', auth.token)
     localStorage.setItem('purrse_refresh_token', auth.refreshToken)
     localStorage.setItem('purrse_username', auth.username)
+    if (auth.displayName) {
+      localStorage.setItem('purrse_display_name', auth.displayName)
+    } else {
+      localStorage.removeItem('purrse_display_name')
+    }
     localStorage.setItem('purrse_expires_at', auth.expiresAt)
   }
 
@@ -45,16 +53,27 @@ export const useAuthStore = defineStore('auth', () => {
     setAuth(data)
   }
 
+  function setDisplayName(name: string | null) {
+    displayName.value = name
+    if (name) {
+      localStorage.setItem('purrse_display_name', name)
+    } else {
+      localStorage.removeItem('purrse_display_name')
+    }
+  }
+
   function logout() {
     token.value = null
     refreshTokenValue.value = null
     username.value = null
+    displayName.value = null
     expiresAt.value = null
     localStorage.removeItem('purrse_token')
     localStorage.removeItem('purrse_refresh_token')
     localStorage.removeItem('purrse_username')
+    localStorage.removeItem('purrse_display_name')
     localStorage.removeItem('purrse_expires_at')
   }
 
-  return { token, username, expiresAt, isAuthenticated, initialize, login, register, refreshToken, logout }
+  return { token, username, displayName, expiresAt, isAuthenticated, initialize, login, register, refreshToken, setDisplayName, logout }
 })