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/codebase/stack.md

@@ -0,0 +1,83 @@
+# Technology Stack
+
+**Analysis Date:** 2026-04-26
+
+## Languages
+
+**Primary:**
+- PHP 7.4+ - All application code (`index.php`, `autoload/`)
+- HTML/PHP - Template files (`templates/`)
+
+**Secondary:**
+- SCSS - Stylesheet authoring (`layout/style-scss/style.scss`)
+- JavaScript (ES5+) - Client-side logic embedded in templates and CDN-loaded libraries
+
+## Runtime
+
+**Environment:**
+- PHP 7.4+ on Apache (shared hosting)
+- MySQL database (`srv81099_brzez_ticket`)
+- Timezone: Europe/Warsaw
+
+**Package Manager:**
+- None — no Composer, no npm
+- All dependencies vendored in `libraries/`
+
+## Frameworks
+
+**Core:**
+- None — custom MVC built from scratch
+
+**Frontend:**
+- Bootstrap 5.2 — Responsive layout and components (CDN)
+- jQuery 3.6 — DOM manipulation and AJAX (CDN)
+- Font Awesome 6.1 — Icons (CDN)
+- Flatpickr — Date picker for ticket date selection (CDN)
+- DataTables — Admin order list pagination/sorting (CDN)
+- html5-qrcode — Browser QR code scanner for on-site validation (CDN)
+
+**Build/Dev:**
+- Live Sass Compiler (VS Code extension) — SCSS → CSS compilation
+- FTP sync via ftp-kr VS Code extension — Deployment
+
+## Key Dependencies
+
+**Critical:**
+- Medoo — MySQL query builder (`libraries/medoo/medoo.php` — referenced in code, may be missing from repo)
+- RedBeanPHP — ORM used in cron jobs (`libraries/rb.php`, 570KB single file)
+- PHPMailer — SMTP email delivery (`libraries/phpmailer/class.phpmailer.php`, `class.smtp.php`)
+- phpqrcode — QR code generation for tickets (`libraries/phpqrcode/qrlib.php`)
+
+**Infrastructure:**
+- PDO — Database access layer (used internally by Medoo)
+- cURL — HTTP calls to Przelewy24 and fakturowo.pl APIs
+
+## Configuration
+
+**Environment:**
+- Single file: `config.php` — contains ALL configuration
+- Database credentials, SMTP settings, ticket pricing, payment gateway keys, admin password
+- No `.env` files — credentials hardcoded (security concern documented in concerns.md)
+
+**Build:**
+- SCSS config in first-line comment of `layout/style-scss/style.scss`
+- No build config files (vite, webpack, etc.)
+
+## Platform Requirements
+
+**Development:**
+- Windows (VS Code with Live Sass Compiler + ftp-kr extensions)
+- PHP 7.4+ locally or via FTP-direct editing
+- MySQL access for schema changes
+
+**Production:**
+- Apache + mod_rewrite (shared hosting via seohost.pl)
+- PHP 7.4+
+- MySQL
+- Outbound SMTP (port 25 to h53.seohost.pl)
+- Outbound HTTPS for Przelewy24 and fakturowo.pl
+
+---
+
+*Stack analysis: 2026-04-26*
+*Update after major dependency changes*