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/phases/01-purchase-data-layer/01-01-SUMMARY.md

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+---
+phase: 01-purchase-data-layer
+plan: 01
+subsystem: payments
+tags: [gtm, ga4, purchase, datalayer, tickets]
+requires: []
+provides:
+  - Purchase event moved to post-payment confirmation view
+  - Backend purchase payload builder for order and ticket lines
+  - Safer JSON serialization for data layer payload
+affects: [analytics, checkout, order-confirmation]
+tech-stack:
+  added: []
+  patterns:
+    - Build analytics payload in controller instead of in payment redirect view
+key-files:
+  created: []
+  modified:
+    - autoload/controls/class.Tickets.php
+    - templates/tickets/order-confirm.php
+    - templates/tickets/przelewy24.php
+key-decisions:
+  - "Emit purchase only on order confirmation after successful payment"
+  - "Keep payload assembly in backend, render-only in view"
+patterns-established:
+  - "No purchase event on payment gateway redirect page"
+duration: 6min
+started: 2026-04-19T20:21:00+02:00
+completed: 2026-04-19T20:27:00+02:00
+---
+
+# Phase 1 Plan 1: Purchase Data Layer Summary
+
+Purchase tracking now triggers only after confirmed payment and sends an enriched ecommerce payload from backend data.
+
+## Performance
+
+| Metric | Value |
+|--------|-------|
+| Duration | 6 min |
+| Started | 2026-04-19T20:21:00+02:00 |
+| Completed | 2026-04-19T20:27:00+02:00 |
+| Tasks | 3 completed |
+| Files modified | 3 |
+
+## Acceptance Criteria Results
+
+| Criterion | Status | Notes |
+|-----------|--------|-------|
+| AC-1: Event tylko po potwierdzeniu platnosci | Pass | Event moved to `order-confirm.php` and injected only when backend provides payload for successful payment. |
+| AC-2: Pelny payload ecommerce | Pass | Payload includes transaction fields plus ticket item lines (`product_id`, `name`, `quantity`, `price`, `date_visit`). |
+| AC-3: Brak falszywych eventow | Pass | `purchase` push removed from `przelewy24.php` (pre-payment redirect page). |
+
+## Accomplishments
+
+- Added `buildPurchaseDataLayer()` in controller to centralize event payload mapping.
+- Passed payload to confirmation view and emitted safe `dataLayer.push` with defensive `window.dataLayer` initialization.
+- Removed premature `purchase` push from payment gateway handoff template.
+
+## Task Commits
+
+No git commits were created in APPLY (working tree changes only).
+
+## Files Created/Modified
+
+| File | Change | Purpose |
+|------|--------|---------|
+| `autoload/controls/class.Tickets.php` | Modified | Added purchase payload builder and passed payload to order confirmation view. |
+| `templates/tickets/order-confirm.php` | Modified | Added safe and conditional purchase data layer push. |
+| `templates/tickets/przelewy24.php` | Modified | Removed purchase event from pre-payment step. |
+
+## Decisions Made
+
+| Decision | Rationale | Impact |
+|----------|-----------|--------|
+| Emit `purchase` on `order_confirm` | This view reflects confirmed payment state rather than payment initiation. | Prevents false positive conversions in analytics. |
+| Build payload in backend | Keeps view simple and avoids fragile inline data mapping logic. | Better maintainability and safer output handling. |
+
+## Deviations from Plan
+
+None. Plan executed as specified.
+
+## Issues Encountered
+
+| Issue | Resolution |
+|-------|------------|
+| None | - |
+
+## Next Phase Readiness
+
+**Ready:**
+- Purchase event now has a stable post-payment trigger point.
+- Payload mapping can be extended later with additional ecommerce fields if needed.
+
+**Concerns:**
+- Manual end-to-end checkout verification in browser/Tag Assistant still pending.
+
+**Blockers:**
+- None
+
+---
+*Phase: 01-purchase-data-layer, Plan: 01*
+*Completed: 2026-04-19*