chore: cleanup legacy files and update gitignore

- Remove obsolete Docker files (will be recreated later)
- Remove legacy launcher.py and transcriptarr.py
- Remove subgen.xml configuration
- Remove test_backend.py (tests will be restructured)
- Remove language_code.py from root (moved to backend/core/)
- Update .gitignore for Python project structure

.gitignore

@@ -9,4 +9,12 @@
 #ignore our settings
 .env
 
-models/
+models/
+
+transcriptarr.db
+
+# Python cache
+__pycache__/
+**/__pycache__/
+*.pyc
+*.pyo