feat: improve notification filters configuration format

- Change filters config from nested dict to simple arrays
- Update NotificationFilters model to use List[str] instead of Dict[str, str]
- Modify notification service to handle list-based filters
- Update API routes and tests for new format
- Update README with new configuration example

Before: [filters.case-insensitive] salary = 'salary'
After: [filters] case-insensitive = ['salary', 'utility']

README.md

@@ -114,9 +114,9 @@ chat_id = 12345
 enabled = true
 
 # Optional: Transaction filters for notifications
-[filters.case-insensitive]
-salary = "salary"
-bills = "utility"
+[filters]
+case-insensitive = ["salary", "utility"]
+case-sensitive = ["SpecificStore"]
 ```
 
 ## 📖 Usage