Add NOK pricing catalog, credit ledger, success-based charging, and tier-gated model routing

- PricingCatalog.php: single source of truth for plans (free/plus/pro), top-ups,
  Stripe price env keys, tool costs (0–6 credits), STT variable billing, feature limits
- FreeTier.php: monthly-first credit deduction, ledger (user_tool_credit_ledger),
  STT reservation/settle/release, monthly reset, trial logic
- StripeClient.php: canonical SKUs (plus/pro/topup_100/300/1000), legacy aliases kept
- stripe-checkout.php: subscription vs payment mode, trial gating, catalog metadata
- stripe-webhook.php: idempotent via stripe_events, handles subscription lifecycle +
  invoice.paid renewal + one-time topup credit grants
- All API tools: success-based credit deduction (check before, charge after)
- transcribe.php: file-size heuristic reservation, settle from actual provider duration
- ask.php + LegalTools.php: ToolModels engine resolution — Pro gets gpt-4o
- KorrespondAgent.php + korrespond.php: tier-gated draft deployment —
  Free/Plus gets gpt-4o-mini, Pro gets gpt-4o
- pricing.php: NOK-only, plan cards, top-up packs, Organisation contact card,
  tool cost table, separate monthly/prepaid balance display
- 003_pricing_credit_catalog.sql: ledger and STT reservation tables

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/translate.php

@@ -55,10 +55,6 @@ try {
     }
 
     $ftUid = dbnToolsFreeTierCheck('translate');
-    $ftRemaining = dbnToolsFreeTierDeduct($ftUid, 'translate');
-    if ($ftRemaining >= 0) {
-        header('X-Credits-Remaining: ' . $ftRemaining);
-    }
 
     $emit('start', [
         'mode'        => 'translate',
@@ -150,6 +146,11 @@ PROMPT;
         'deployment'  => 'gpt-4o-mini',
     ]);
 
+    $ftRemaining = dbnToolsFreeTierDeduct($ftUid, 'translate');
+    if ($ftRemaining >= 0) {
+        $result['balance'] = $ftRemaining;
+    }
+
     $emit('final', ['result' => $result]);
 
 } catch (DbnToolsHttpException $e) {