feat(auth): two-role permission system (admin/member)

Adds an admin/member role to WebUI auth. /api/users and /api/audit
are now gated by a requireAdmin middleware; all other authenticated
endpoints accept both roles. Schema migration defaults all existing
users to admin to preserve access. POST /api/users defaults new users
to member; first-run setup always creates an admin. Adds PATCH
/api/users/:id/role with last-admin demotion and deletion guards.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/web/websocket-auth.test.ts

@@ -36,7 +36,7 @@ describe("WebSocket auth at upgrade", () => {
     botDb = createDatabase(":memory:");
     const users = createUserStore(botDb.db);
     const sessions = createSessionStore(botDb.db);
-    const u = await users.createUser("alice", "pw");
+    const u = await users.createUser("alice", "pw-alice", "admin");
     validToken = sessions.createSession(u.id).token;
 
     const { server } = buildServer(sessions);