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/korrespond.php

@@ -3,6 +3,7 @@ declare(strict_types=1);
 
 require_once __DIR__ . '/../includes/bootstrap.php';
 require_once __DIR__ . '/../includes/KorrespondAgent.php';
+require_once __DIR__ . '/../includes/ToolModels.php';
 
 dbnToolsRequireMethod('POST');
 dbnToolsRequireAuth();
@@ -165,11 +166,12 @@ try {
 
     // ── Deduct credit now (Pass 2 starts) ───────────────────────────────────────
     $ftUid = dbnToolsFreeTierCheck('korrespond');
+    $engine = ToolModels::engineForUser($ftUid, 'azure_mini');
     $ftRemaining = dbnToolsFreeTierDeduct($ftUid, 'korrespond');
     $creditDeducted = true;
 
     // ── Pass 2: retrieve law → draft → self-check → translate ──────────────────
-    $result = $agent->generate($intake, $classify, $emit);
+    $result = $agent->generate($intake, $classify, $emit, $engine);
     $result['ok']         = true;
     $result['latency_ms'] = (int)round((microtime(true) - $startTime) * 1000);
     if ($ftRemaining >= 0) {
@@ -182,7 +184,7 @@ try {
         'ok'           => true,
         'latency_ms'   => $result['latency_ms'],
         'source_count' => is_array($result['cited_law'] ?? null) ? count($result['cited_law']) : 0,
-        'deployment'   => 'gpt-4o',
+        'deployment'   => ($engine === 'azure_full') ? 'gpt-4o' : 'gpt-4o-mini',
     ]);