chore: reorganize persistent data into ./data folder

- Move all persistent data (instance, uploads, caddy configs) to ./data folder
- Update docker-compose.yml volumes to use ./data structure
- All data is now centralized for easier backup and portability
- Simplify volume management by removing named volumes
- Add data folder to .gitignore

.gitignore

@@ -13,6 +13,9 @@ ENV/
 instance/
 .webassets-cache
 
+# Persistent data folder (containers, database, uploads)
+data/
+
 # IDEs
 .vscode/
 .idea/
@@ -52,3 +55,7 @@ htmlcov/
 dist/
 build/
 *.egg-info/
+
+#data
+data/
+