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/i18n.php

@@ -233,7 +233,7 @@ function dbnToolsTranslations(): array
             'nav_logout'          => 'Log out',
             'credits_available'   => 'Available credits',
             'credits_monthly'     => 'monthly',
-            'credits_bonus'       => 'bonus',
+            'credits_bonus'       => 'prepaid',
             'details_link'        => 'Details',
             'my_case'             => 'My case',
             'build_your_case'     => 'Build your own case',
@@ -678,7 +678,7 @@ function dbnToolsTranslations(): array
             'nav_logout'          => 'Logg ut',
             'credits_available'   => 'Tilgjengelige kreditter',
             'credits_monthly'     => 'månedlige',
-            'credits_bonus'       => 'bonus',
+            'credits_bonus'       => 'forhåndsbetalte',
             'details_link'        => 'Detaljer',
             'my_case'             => 'Min sak',
             'build_your_case'     => 'Bygg din egen sak',