feat(01-purchase-data-layer): add post-payment purchase data layer

Phase 1 complete:

- move purchase event to order confirmation after successful payment

- add backend purchase payload builder for transaction and ticket lines

- remove premature purchase push from przelewy24 redirect view

.paul/config.md

@@ -0,0 +1,33 @@
+# Project Config
+
+**Project:** bilety.brzezovka.pl
+**Created:** 2026-04-19 20:20
+
+## Project Settings
+
+```yaml
+project:
+  name: bilety.brzezovka.pl
+  version: 0.0.0
+```
+
+## Integrations
+
+### SonarQube
+
+```yaml
+sonarqube:
+  enabled: false
+  reason: "User skipped during init"
+```
+
+## Preferences
+
+```yaml
+preferences:
+  auto_commit: false
+  verbose_output: false
+```
+
+---
+*Config created: 2026-04-19 20:20*