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/stripe-checkout.php

@@ -16,12 +16,9 @@ if ($userId <= 0 || $email === '') {
 }
 
 $input = dbnToolsJsonInput(2000);
-$sku = (string)($input['sku'] ?? '');
+$sku = StripeClient::canonicalSku((string)($input['sku'] ?? ''));
 
-$validSubscriptions = ['plus', 'pro'];
-$validTopups = ['topup_s', 'topup_m', 'topup_l'];
-
-if (!in_array($sku, array_merge($validSubscriptions, $validTopups), true)) {
+if (!StripeClient::isSubscriptionSku($sku) && !StripeClient::isTopupSku($sku)) {
     dbnToolsError('Unknown SKU.', 400, 'unknown_sku');
 }
 
@@ -33,7 +30,18 @@ try {
     $successUrl = $baseUrl . '/billing.php?status=success&session_id={CHECKOUT_SESSION_ID}';
     $cancelUrl  = $baseUrl . '/pricing.php?status=canceled';
 
-    $isSub = in_array($sku, $validSubscriptions, true);
+    $isSub = StripeClient::isSubscriptionSku($sku);
+    $credits = $isSub ? 0 : StripeClient::topupCredits($sku);
+    $metadata = [
+        'user_id' => (string)$userId,
+        'sku' => $sku,
+        'catalog_version' => PricingCatalog::VERSION,
+    ];
+    if ($isSub) {
+        $metadata['tier'] = $sku;
+    } else {
+        $metadata['credits'] = (string)$credits;
+    }
 
     $params = [
         'mode' => $isSub ? 'subscription' : 'payment',
@@ -44,10 +52,7 @@ try {
             'price'    => StripeClient::priceId($sku),
             'quantity' => 1,
         ]],
-        'metadata' => [
-            'user_id' => (string)$userId,
-            'sku'     => $sku,
-        ],
+        'metadata' => $metadata,
         'allow_promotion_codes' => true,
         'billing_address_collection' => 'auto',
         'locale' => 'auto',
@@ -58,10 +63,11 @@ try {
         FreeTier::ensureRow($userId);
         $detail = FreeTier::balanceDetail($userId);
         $params['subscription_data'] = [
-            'metadata' => ['user_id' => (string)$userId, 'tier' => $sku],
+            'metadata' => $metadata,
         ];
-        if ($sku === 'plus' && empty($detail['trial_started_at'])) {
-            $params['subscription_data']['trial_period_days'] = 14;
+        $trialDays = PricingCatalog::planTrialDays($sku);
+        if ($trialDays > 0 && empty($detail['trial_started_at'])) {
+            $params['subscription_data']['trial_period_days'] = $trialDays;
             $params['subscription_data']['trial_settings'] = [
                 'end_behavior' => ['missing_payment_method' => 'cancel'],
             ];
@@ -69,7 +75,7 @@ try {
         $params['payment_method_collection'] = 'always';
     } else {
         $params['payment_intent_data'] = [
-            'metadata' => ['user_id' => (string)$userId, 'sku' => $sku, 'credits' => (string)StripeClient::topupCredits($sku)],
+            'metadata' => $metadata,
         ];
     }