fix: harden auth, cron secrets, and provider flows (GNU-17) (#148)

- Replace === with crypto.timingSafeEqual in all 7 cron routes via shared lib/auth/cron.ts
- Add in-memory rate limiting (60 req/min) and expires_at support to calendar feed
- Add exponential backoff on MFA verify after 3 failed attempts
- Add 60s cooldown on password reset requests
- Validate bank callback auth code format before API call
- Redact session IDs from bank sync and callback logs
- Validate OAuth redirect_uris against allowlist (claude.ai, claude.com, localhost)
- Remove excessive PII/debug console logging from login page

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/api/extensions/enable-banking/sync/cron/route.ts

@@ -10,6 +10,7 @@ import {
   generateConsentExpiryEmailSubject,
 } from '@/lib/email/consent-notification-templates'
 import { ensureInitialized } from '@/lib/init'
+import { verifyCronSecret } from '@/lib/auth/cron'
 import type { StoredAccount } from '@/extensions/general/enable-banking/types'
 
 ensureInitialized()
@@ -24,13 +25,8 @@ ensureInitialized()
  * Deduplication via external_id makes repeated runs safe.
  */
 export async function GET(request: Request) {
-  // Verify cron secret
-  const authHeader = request.headers.get('authorization')
-  const cronSecret = process.env.CRON_SECRET
-
-  if (!cronSecret || authHeader !== `Bearer ${cronSecret}`) {
-    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
-  }
+  const authError = verifyCronSecret(request)
+  if (authError) return authError
 
   const supabaseUrl = process.env.NEXT_PUBLIC_SUPABASE_URL
   const supabaseServiceKey = process.env.SUPABASE_SERVICE_ROLE_KEY
@@ -212,7 +208,7 @@ export async function GET(request: Request) {
         connectionId: connection.id,
         userId: connection.user_id,
         bankName: connection.bank_name,
-        sessionId: connection.session_id,
+        sessionId: '[REDACTED]',
         consentExpires: connection.consent_expires,
         lastSyncedAt: connection.last_synced_at,
         message,