fix(payroll): Refactor /collect endpoint and add To-Do.md

This commit addresses several issues in the `/collect` endpoint to improve its security and robustness. It also introduces a `To-Do.md` file as requested by the user.

Key changes:
- Refactored the `/collect` endpoint to use a single database transaction, preventing data inconsistencies.
- Fixed SQL injection vulnerabilities by converting all database queries to use parameterized statements.
- Corrected a `TypeError` by ensuring the `COLLECT_COOLDOWN` configuration variable is always an integer.
- Updated transaction logging to record 'SYSTEM' as the source of funds for salary collections, instead of a "NULL" string.
- Added a `To-Do.md` file with suggestions for future features, including an automated payroll system, user transaction history, and an admin panel.

config.py

@@ -18,4 +18,4 @@ class Config:
 
     # Admin
     ADMIN_KEY = os.getenv('ADMIN_KEY')
-    COLLECT_COOLDOWN = os.getenv('COLLECT_COOLDOWN')
+    COLLECT_COOLDOWN = int(os.getenv('COLLECT_COOLDOWN', 24))