auth: sign-in ways, sign-in mode, and the admin who keeps a password (S1)

Spec 12 S1: migration 0012 (password_hash nullable, user_identities, sessions.method and the
OpenID token columns), auth.mode (only "password" until S2), GET /api/auth/methods, login body
{login, password} (email still accepted), signIn on users and /api/auth/me, a Signs in with
column on Users. The last active admin with a password can't be deleted, disabled or demoted.

apps/api/src/auth/sessions.ts

@@ -32,6 +32,7 @@ export async function createSession(
   userId: string,
   ip: string | null,
   userAgent: string | null,
+  method: 'password' | 'ldap' | 'oidc' = 'password',
 ): Promise<string> {
   const token = randomBytes(32).toString('base64url');
   await db.insert(sessions).values({
@@ -40,6 +41,7 @@ export async function createSession(
     expiresAt: new Date(Date.now() + LIFETIME),
     ip,
     userAgent: userAgent?.slice(0, 500) ?? null,
+    method,
   });
   return token;
 }