feat: add LDAP support and guest user functionality

- Introduced BaseDN configuration for LDAP in the config.
- Enhanced User model to include IsLDAP field.
- Updated database queries to handle LDAP users.
- Implemented GraphQL queries for LDAP browsing and user authentication type.
- Added ACL management for users and groups, including guest user permissions.
- Updated frontend to support LDAP login and guest user login.
- Improved error handling and user feedback in login and ACL management.

backend/internal/graph/schema.graphql

@@ -33,10 +33,16 @@ type Query {
   images(slug: String!): [ImageFile!]!
 
   # Browse LDAP tree (admin only)
-  ldapBrowse(url: String, adminUser: String, adminPass: String): LDAPTree!
+  ldapBrowse(url: String, baseDN: String, adminUser: String, adminPass: String): LDAPTree!
 
   # Fetch permissions for a path
   acl(path: String!): [ACLEntry!]!
+
+  # Returns all users and groups that can be assigned to ACL entries (admin only).
+  aclSubjects: ACLSubjects!
+
+  # Returns "local", "ldap", or "guest" for a given username.
+  userAuthType(username: String!): String!
 }
 
 type Mutation {
@@ -47,7 +53,7 @@ type Mutation {
   testLdapConnection(url: String!, adminUser: String, adminPass: String): LDAPTestResult!
 
   # Authenticate and receive a bearer token.
-  login(username: String!, password: String!): String!
+  login(username: String!, password: String!, ldapPassword: String): String!
 
   # Invalidate the current session.
   logout: Boolean!
@@ -101,6 +107,7 @@ type AppConfig {
 
 type LDAPConfig {
   url:       String!
+  baseDN:    String!
   adminUser: String!
 }
 
@@ -179,8 +186,20 @@ input SetupInput {
 
 input LDAPInput {
   url:       String!
+  baseDN:    String
   adminUser: String!
-  adminPass: String!
+  adminPass: String
+}
+
+type ACLSubject {
+  id:     Int!
+  name:   String!
+  isLdap: Boolean!
+}
+
+type ACLSubjects {
+  users:  [ACLSubject!]!
+  groups: [ACLSubject!]!
 }
 
 input ACLInput {