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>

includes/LegalTools.php

@@ -186,8 +186,9 @@ final class DbnLegalToolsService
         ];
     }
 
-    public function ask(string $question, string $language = 'en'): array
+    public function ask(string $question, string $language = 'en', string $engine = 'azure_mini'): array
     {
+        $engine = in_array($engine, ['azure_mini', 'azure_full'], true) ? $engine : 'azure_mini';
         $search = $this->search($question, $language, 7);
         $hits = $search['hits'];
         $trace = $search['trace'];
@@ -240,7 +241,8 @@ Return JSON only with these keys:
 PROMPT;
 
         $system = $this->legalJsonSystemPrompt($language);
-        $raw = $this->azure->chatText([
+        $askDeployment = ($engine === 'azure_full') ? 'gpt-4o' : 'gpt-4o-mini';
+        $raw = $this->azure->withDeployment($askDeployment)->chatText([
             ['role' => 'system', 'content' => $system],
             ['role' => 'user', 'content' => $prompt],
         ], [
@@ -278,7 +280,7 @@ PROMPT;
             'trace_metadata' => [
                 'chunk_count' => count($hits),
                 'source_count' => count($hits),
-                'deployment' => $this->azure->chatDeployment(),
+                'deployment' => $askDeployment,
                 'citation_confidence' => $search['trace_metadata']['citation_confidence'] ?? 'medium',
             ],
             'disclaimer' => dbnToolsDisclaimer($language),