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/legal-analysis.php

@@ -20,6 +20,8 @@ header('X-Accel-Buffering: no');
 $startTime = microtime(true);
 $language  = 'en';
 $creditDeducted = false;
+$ftUid = 0;
+$ftRemaining = -1;
 
 $emit = function (string $event, array $payload = []) use ($startTime): void {
     $payload['event'] = $event;
@@ -44,6 +46,7 @@ try {
             422, 'empty_text'
         );
     }
+    $ftUid = dbnToolsFreeTierCheck('legal-analysis');
 
     $emit('start', [
         'mode'     => 'legal-analysis',
@@ -75,12 +78,8 @@ try {
     }
 
     // Deduct credit (gated until extract succeeds and at least one issue exists)
-    $ftUid = dbnToolsFreeTierCheck('legal-analysis');
     $ftRemaining = dbnToolsFreeTierDeduct($ftUid, 'legal-analysis');
     $creditDeducted = true;
-    if ($ftRemaining >= 0) {
-        header('X-Credits-Remaining: ' . $ftRemaining);
-    }
 
     $emit('issues_extracted', [
         'count'  => count($issues),
@@ -129,6 +128,9 @@ try {
         'model'              => 'dbn-legal-agent-v3',
         'latency_ms'         => (int)round((microtime(true) - $startTime) * 1000),
     ];
+    if ($ftRemaining >= 0) {
+        $result['balance'] = $ftRemaining;
+    }
 
     dbnToolsLogMetadata([
         'tool'         => 'legal-analysis',