[Feature] Create Nostr Settings Management Screen

[TheRealCheebs]

Problem Statement

Users need a centralized place to configure Nostr-specific settings beyond relays, including identity management and protocol preferences.

Proposed Solution

1. Create settings screen with sections for:
   • Identity management (key generation, import/export)
   • Protocol preferences (NIPs, default behaviors)
   • Privacy settings
   • Data management
2. Implement secure key storage
3. Add settings persistence

Acceptance Criteria

• Users can generate new Nostr identity
• Private keys can be imported/exported securely
• Protocol preferences configurable (NIP-05, NIP-19, etc.)
• Data management options (clear cache, reset settings)
• Settings persist across app restarts

Technical Notes

• Use Android Keystore for secure key storage
• Implement settings using DataStore
• Add QR code scanning for key import
• Consider biometric protection for sensitive operations

Tasks

• Design settings screen layout
• Implement identity management
• Add protocol preference toggles
• Create secure key storage
• Implement data management functions
• Add settings export/import

Additional Context

Follow Nostr NIPs for identity and key handling best practices.

Checklist

• I've searched existing issues to ensure this isn't a duplicate
• This is a single feature request (not multiple unrelated requests)