Add secrets management functionality and UI enhancements

[TerminallyLazy]

• Introduced SecretsManager class for handling secret values, including loading, saving, and masking.
• Updated agent and tool classes to mask secrets in logs and responses.
• Added a secrets management section in settings with a full-screen modal for editing secrets.
• Enhanced UI with a new modal for secrets input and improved textarea functionality.
• Adjusted requirements and added necessary imports across multiple files.