Add monetization spine + Build Your Own Case (Min Sak)

- Stripe: StripeClient.php, checkout/portal/webhook endpoints, idempotent event handling
- FreeTier: tier-aware credits (free/light/pro/pro_plus), bonus_balance, hourly caps per tier
- pricing.php + billing.php: 4-tier cards, 3 topups, Customer Portal, balance breakdown
- Min Sak: CaseStore.php, AzureDocIntelligence.php, AzureSearchAdmin.php — per-user hybrid RAG
- api/case/: upload, list, delete, ingest-callback (HMAC-auth'd from n8n)
- award-survey-credits: inter-site HMAC endpoint for dobetternorge.no survey bonus
- dashboard.php: tier badge, balance breakdown card, Min Sak CTA, survey CTA
- KorrespondAgent + all 3 other agents: use_my_case toggle wired to dbnToolsCaseContext()
- bootstrap.php: dbnToolsCaseContext(), dbnToolsIntersiteSecret(), dbnToolsCurrentTier()

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

api/stripe-portal.php

@@ -0,0 +1,36 @@
+<?php
+declare(strict_types=1);
+
+require_once __DIR__ . '/../includes/bootstrap.php';
+require_once __DIR__ . '/../includes/StripeClient.php';
+require_once __DIR__ . '/../includes/FreeTier.php';
+
+dbnToolsRequireMethod('POST');
+dbnToolsRequireAuth();
+
+$user = dbnToolsAuthenticatedUser();
+$userId = (int)($user['user_id'] ?? 0);
+if ($userId <= 0) {
+    dbnToolsError('User session missing user_id.', 401, 'bad_session');
+}
+
+$row = FreeTier::row($userId);
+$customerId = (string)($row['stripe_customer_id'] ?? '');
+if ($customerId === '') {
+    // No Stripe customer yet — happens if user never checked out.
+    dbnToolsError('No Stripe customer on record. Subscribe first.', 400, 'no_customer');
+}
+
+try {
+    $stripe = new StripeClient();
+    $baseUrl = (dbnToolsIsHttps() ? 'https://' : 'http://') . ($_SERVER['HTTP_HOST'] ?? 'tools.dobetternorge.no');
+    $session = $stripe->createPortalSession($customerId, $baseUrl . '/billing.php');
+    $url = (string)($session['url'] ?? '');
+    if ($url === '') {
+        dbnToolsError('Stripe did not return a portal URL.', 502, 'stripe_no_url');
+    }
+    dbnToolsRespond(['ok' => true, 'url' => $url]);
+} catch (Throwable $e) {
+    error_log('[stripe-portal] ' . $e->getMessage());
+    dbnToolsError('Could not open billing portal: ' . $e->getMessage(), 500, 'stripe_failed');
+}