Make basic auth and SSO mutually exclusive per host; fix silently-broken validation errors

- Auth tab is now a single choice (Off / Basic auth / SSO) instead of two
  independent toggles that could both be on at once, which made it
  ambiguous which gate actually protected a request. Enforced both in the
  UI and server-side (POST/PUT), accounting for partial PUT updates against
  the existing record.
- Add per-user basic-auth management (change password, delete) so an admin
  no longer has to blow away and retype the whole user list to remove or
  rotate one account.
- Fix: `Model.errors.ObjectValidateError(...)` is a constructor and was
  being called without `new` everywhere in this codebase. Without `new`,
  `this` inside it was the module's shared `errors` object (mutated in
  place) and the call evaluated to `undefined` — so every
  `throw Model.errors.ObjectValidateError(...)` actually threw `undefined`,
  which Express's `next(undefined)` treats as "no error" and silently
  falls through to the catch-all 404 handler. Every host/user/group/
  permission/dns-provider validation error (bad hostname, bad IP, etc.) was
  showing a confusing "Page not found" instead of the real message.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

nodejs/models/local_group.js

@@ -30,7 +30,7 @@ class LocalGroup extends Table{
 	static async create(data){
 		data.name = this.slug(data.name);
 		if(!data.name){
-			throw this.errors.ObjectValidateError([{key: 'name', message: 'A group name is required.'}]);
+			throw new this.errors.ObjectValidateError([{key: 'name', message: 'A group name is required.'}]);
 		}
 		if(!Array.isArray(data.members)) data.members = [];
 		return super.create(data);
@@ -39,7 +39,7 @@ class LocalGroup extends Table{
 	async addMember(username){
 		username = String(username || '').trim();
 		if(!username){
-			throw this.constructor.errors.ObjectValidateError([{key: 'username', message: 'A username is required.'}]);
+			throw new this.constructor.errors.ObjectValidateError([{key: 'username', message: 'A username is required.'}]);
 		}
 		let members = Array.isArray(this.members) ? this.members : [];
 		if(members.includes(username)) return this;