feat: Add type hints to management scripts

[db-tycoon-stephen]

Problem

Only 1 of 35 scripts has type hints. This reduces IDE support, makes debugging harder, and is inconsistent with modern Python practices.

Scope

Add type hints to the 18 core management scripts:

• manage_warehouses.py, cost_optimization.py, security_audit.py, backup_restore.py
• monitor_health.py, monitor_audit.py, monitor_metrics.py, monitor_logs.py
• apply_schema_grants.py, validate_schema_grants.py
• manage_users.py, user_create.py, generate_user_from_issue.py
• deploy_safe.py, github_issue_to_snowddl.py
• generate_passwords.py, generate_rsa_keys_batch.py
• health_check.py

Acceptance Criteria

• All management scripts have function signatures with type hints
• Return types annotated
• Key dataclass/dict parameters typed
• No mypy errors on annotated code