fix: inline getDatabasePath into Database.php, delete config/config.php

- Remove require_once for config/config.php (file was never deployed — outside app/)
- Inline DB path resolution directly in Database::determineDatabasePath()
- Uses APP_ROOT when defined (bootstrap already loaded), falls back to __DIR__/../
- DB_ENV=test|prod env-var override preserved for tests
- php -S cli-server -> test.db, nginx/fpm -> posterg.db

TODO.md

@@ -57,6 +57,8 @@
 - [x] Update Dispatcher to render full pages (head + header + view + footer) instead of requiring bootstrap
 - [x] Ensure admin/index.php bootstraps its own path (not affected by front controller)
 
+- [x] Fix config/config.php path mess — inline getDatabasePath() into Database.php, delete config/config.php
+
 ### Phase 3: Server config
 - [ ] Update router.php — route all PHP requests to Dispatcher
 - [ ] Update nginx config — point all public routes to index.php via try_files