Add engagement authorization, remove price headers from intake pages, fix duplicate emails

- Add clickwrap authorization checkbox to fcc-compliance, state-puc, neca-ocn order pages
- Store engagement_accepted_at/ip/version in compliance_orders (migration 074)
- Add 499-A past-due/multi-year eSign engagement letter generator
- Gate 499-A handler on engagement signature for past-due/multi-year orders
- Remove price/tax/fee headers from all 19 intake pages (post-payment only)
- Fix duplicate confirmation email for compliance_batch orders
- Add USAC past-due fee negotiation research doc

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

api/src/routes/checkout.ts

@@ -1462,7 +1462,11 @@ export async function handlePaymentComplete(
   }
 
   // ── Send order confirmation email ──────────────────────────────────────
-  try {
+  // Skip for compliance_batch — sendComplianceIntakeEmail already sent
+  // a combined confirmation + intake email above.
+  if (order_type === "compliance_batch") {
+    console.log(`[checkout] Skipping generic confirmation for ${order_id} — intake email already sent`);
+  } else try {
     await sendOrderConfirmationEmail({
       order_id,
       order_type,