docs: map existing codebase

- stack.md - Technologies and dependencies
- architecture.md - System design and patterns
- structure.md - Directory layout
- conventions.md - Code style and patterns
- testing.md - Test structure (none)
- integrations.md - External services
- concerns.md - Technical debt and issues
- db_schema.md - Database schema and relationships

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

.paul/STATE.md

@@ -29,6 +29,10 @@ PLAN --> APPLY --> UNIFY
 
 ## Accumulated Context
 
+### Codebase Mapped
+Date: 2026-04-26
+Documents: `.paul/codebase/` (8 files — stack, architecture, structure, conventions, testing, integrations, concerns, db_schema)
+
 ### Decisions
 - 2026-04-19: Event `purchase` emitowany na `order-confirm`, nie na `przelewy24` (eliminuje falszywe konwersje).
 - 2026-04-19: Payload ecommerce budowany w backendzie i serializowany bezpiecznie do widoku.