fix(security): harden 2FA setup, OIDC default role, and rate-limit fallback (v0.17.3-beta)

Address the actionable findings from an adversarial review:

- 2FA enrollment now requires the current password (/totp/setup), so a
  hijacked session or XSS can't enable TOTP and lock the real user out.
  SSO-only accounts (no local password) are told to set one first. Frontend
  collects the password before starting setup.
- OIDC config rejects default_role='admin': auto-provisioning unmatched users
  straight to admin is almost never intended — admin must come from an explicit
  group → role mapping.
- Rate limiter no longer fails fully open on a Redis outage. Redis calls are
  bounded by an 800ms timeout (the client uses maxRetriesPerRequest:null, so
  commands would otherwise hang, not throw), and on failure a per-process
  in-memory sliding-window fallback keeps /login and other limited endpoints
  throttled. Verified with Redis stopped: attempts throttle (429) instead of
  hanging or passing unlimited.

Findings intentionally not actioned: the "API-token auth is fire-and-forget"
report was a false positive (Express awaits next(), which is called inside the
promise), and the webhook DB-pool and JWT-revocation items are either
overstated or a separate architectural decision.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/pages/SettingsPage.tsx

@@ -137,6 +137,7 @@ export default function SettingsPage() {
   // ─── TOTP / 2FA ────────────────────────────────────────────────────────────
   const [totpSetupData, setTotpSetupData] = useState<{ secret: string; uri: string; qr: string } | null>(null);
   const [totpConfirmCode, setTotpConfirmCode] = useState('');
+  const [totpSetupPassword, setTotpSetupPassword] = useState('');
   const [totpDisablePassword, setTotpDisablePassword] = useState('');
   const [totpMsg, setTotpMsg] = useState('');
   const [totpError, setTotpError] = useState('');
@@ -148,8 +149,8 @@ export default function SettingsPage() {
   });
 
   const startTotpSetupMutation = useMutation({
-    mutationFn: () => authApi.totpSetup(),
-    onSuccess: (res) => { setTotpSetupData(res.data); setTotpConfirmCode(''); setTotpError(''); },
+    mutationFn: () => authApi.totpSetup(totpSetupPassword),
+    onSuccess: (res) => { setTotpSetupData(res.data); setTotpConfirmCode(''); setTotpSetupPassword(''); setTotpError(''); },
     onError: (err: unknown) => {
       const msg = (err as { response?: { data?: { error?: string } } })?.response?.data?.error;
       setTotpError(msg || 'Failed to start TOTP setup');
@@ -1157,14 +1158,26 @@ export default function SettingsPage() {
               </div>
             ) : (
               /* Not enabled, not in setup */
+              <div className="space-y-3">
+                <div>
+                  <label className="label">Confirm your password to set up 2FA</label>
+                  <input
+                    type="password"
+                    className="input max-w-xs"
+                    value={totpSetupPassword}
+                    onChange={(e) => setTotpSetupPassword(e.target.value)}
+                    autoComplete="current-password"
+                  />
+                </div>
               <button
                 onClick={() => startTotpSetupMutation.mutate()}
-                disabled={startTotpSetupMutation.isPending}
+                disabled={!totpSetupPassword || startTotpSetupMutation.isPending}
                 className="btn-primary"
               >
                 <ShieldCheck className="w-4 h-4" />
                 Set up 2FA
               </button>
+              </div>
             )}
           </div>
         </div>