Add roles and a user management tab for admins (#180, #179)

Until now every account could do the same, and managing accounts
meant running make-user.php on the server. Accounts now carry a role,
and admins get a tab in the editor to create, rename, re-role, reset
and delete accounts. Both issues share the same server files, so they
land in one commit.

#180 Roles:
- Every account is admin or user. A missing or unknown role counts as
  user, on the server and in the client.
- auth/session and auth/login return {user, role}.
- Auth::requireAdmin() answers everyone else with 403.
- make-user.php takes the role as a third argument. Without it an
  existing account keeps its role, so a password reset from the CLI
  never demotes an admin.
- Admins see and save other users' projects like their own. Saving
  keeps the original owner.

#179 User management:
- The account menu gets "User management" (admins only) and "Plugins"
  (everyone). Both open the same closable tab, accounts on top and
  plugins below. The fixed Plugins tab is gone.
- Per account: Rename, Role, Password (no old password needed) and
  Delete with a confirmation. "New user..." creates one.
- Each account lists its projects with an Open button.
- Delete is refused while the account still owns projects.
- Renaming moves the projects along and ends every session of the
  account. transfer takes the same lock as save.
- On their own row an admin can only set the password. The last admin
  cannot be demoted or deleted. The server enforces both.
- The account rules live in AccountRules.php and accountRules.ts as
  pure functions, so they are testable without a server.

Findings:
- At 1280 px the Delete button reached past the column edge and was
  not clickable. The name column is flexible now, and module 49 checks
  the layout.
- The server lets an admin delete other users' projects, but the
  editor has no button for it yet. Left open in the issue.

Tests:
- ./check.sh: 148 files, 2214 tests, exit 0 (was 147 / 2204).
- New tests/php/accounts.test.php, 51 checks, plain PHP. CI runs it
  as its own step in the gate job, the host has no PHP.
- New e2e module 49 with 18 checks. CI creates the e2e-admin account
  in serve.sh. Modules 14, 38, 46 and the scaffold follow the new tab.
- e2e 1-16,37,38,45,46,49: all passed, 581 checks.
- Counter-checks: owner on save, admin view, default role and self
  delete in PHP fail 7, 5, 5 and 1 checks. Unchecked requireAdmin,
  a wider column and the caller as owner each fail exactly their
  e2e check.
- Check sum 1314 -> 1333 (+1 in 38, +18 in 49), computed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/editor/auth/LoginScreen.ts

@@ -1,5 +1,5 @@
 import { Graphics } from 'pixi.js';
-import { type AuthStore, WrongCredentialsError } from '../../core/store/AuthStore';
+import { type AuthStore, type SignedIn, WrongCredentialsError } from '../../core/store/AuthStore';
 import { Button, drawControlBox, Label, Spacer, TextField, Theme, ui, VStack } from '../../ui';
 import { FormStatus, refocus } from './FormStatus';
 import { loginError, loginProblem } from './loginRules';
@@ -40,7 +40,7 @@ export class LoginScreen extends VStack {
 
   constructor(
     private readonly auth: AuthStore,
-    private readonly onSignedIn: (user: string) => void,
+    private readonly onSignedIn: (account: SignedIn) => void,
   ) {
     super({ align: 'center', gap: Theme.gap });
     this.add(new Spacer(), 1);
@@ -101,8 +101,7 @@ export class LoginScreen extends VStack {
     }
     this.status.setBusy(true);
     try {
-      const user = await this.auth.logIn(username, password);
-      this.onSignedIn(user);
+      this.onSignedIn(await this.auth.logIn(username, password));
     } catch (error) {
       this.status.say(loginError(error, error instanceof WrongCredentialsError));
       this.status.setBusy(false);