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/discrepancy.php

@@ -8,7 +8,6 @@ require_once __DIR__ . '/../includes/ToolModels.php';
 dbnToolsRequireMethod('POST');
 dbnToolsRequireAuth();
 $ftUid       = dbnToolsFreeTierCheck('discrepancy');
-$ftRemaining = dbnToolsFreeTierDeduct($ftUid, 'discrepancy');
 
 @ini_set('output_buffering', '0');
 @ini_set('zlib.output_compression', '0');
@@ -19,7 +18,6 @@ ob_implicit_flush(true);
 header('Content-Type: application/x-ndjson; charset=utf-8');
 header('Cache-Control: no-store');
 header('X-Accel-Buffering: no');
-if ($ftRemaining >= 0) { header('X-Credits-Remaining: ' . $ftRemaining); }
 
 $language  = 'en';
 $startTime = microtime(true);
@@ -146,6 +144,10 @@ try {
         'deployment'     => $result['trace_metadata']['deployment'] ?? null,
     ]);
 
+    $ftRemaining = dbnToolsFreeTierDeduct($ftUid, 'discrepancy');
+    if ($ftRemaining >= 0) {
+        $result['balance'] = $ftRemaining;
+    }
 
     $emit('final', ['result' => $result]);