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>

api/lib/Auth.php

@@ -29,6 +29,26 @@ final class Auth
         return $user;
     }
 
+    /**
+     * The signed-in user if they are an administrator (#180), else 401 or 403. Every route that
+     * may do more than a user goes through here: the editor only hides what it may not offer, the
+     * decision is made on this side.
+     */
+    public function requireAdmin(): string
+    {
+        $user = $this->require();
+        if ($this->users->role($user) !== 'admin') {
+            Response::error('Administrators only', 403);
+        }
+        return $user;
+    }
+
+    /** `admin` or `user`; the session answer carries it so the editor knows what to offer. */
+    public function role(string $user): string
+    {
+        return $this->users->role($user);
+    }
+
     /** Checks the pair, starts a session and sets the cookie. Null when the pair is wrong. */
     public function logIn(string $username, string $password): ?string
     {
@@ -68,6 +88,22 @@ final class Auth
         return true;
     }
 
+    /**
+     * An administrator sets somebody's password without knowing the old one (#179). That account's
+     * sessions end with it, except the one asking when it is their own.
+     */
+    public function resetPassword(string $user, string $new): void
+    {
+        $this->users->put($user, $new);
+        $this->sessions->destroyAllFor($user, $this->token());
+    }
+
+    /** Signs an account out everywhere – it was renamed or deleted, and its sessions carry the old name. */
+    public function endSessionsOf(string $user): void
+    {
+        $this->sessions->destroyAllFor($user);
+    }
+
     private function token(): string
     {
         return (string) ($_COOKIE[SessionStore::COOKIE] ?? '');