feat: Implement comprehensive Nostr identity and social features

## Core Identity Management
- Add secure key generation and import functionality
- Implement AES-GCM encryption with PBKDF2 key derivation
- Create password-protected identity storage
- Add browser-compatible crypto utilities (no Buffer dependency)

## User Interface
- Build identity management dialog with tabs for setup and profile
- Add navbar integration with user dropdown and mobile support
- Create password unlock dialog for encrypted identities
- Integrate vue-sonner for toast notifications

## Nostr Protocol Integration
- Implement event creation (notes, reactions, profiles, contacts)
- Add reply thread detection and engagement metrics
- Create social interaction composables for publishing
- Support multi-relay publishing with failure handling
- Add profile fetching and caching system

## Security Features
- Web Crypto API with 100k PBKDF2 iterations
- Secure random salt and IV generation
- Automatic password prompts for encrypted storage
- Legacy support for unencrypted identities

## Technical Improvements
- Replace all Buffer usage with browser-native APIs
- Add comprehensive error handling and validation
- Implement reactive state management with Vue composables
- Create reusable crypto utility functions

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/lib/utils.ts

@@ -13,3 +13,6 @@ export function valueUpdater<T extends Updater<any>>(updaterOrValue: T, ref: Ref
       ? updaterOrValue(ref.value)
       : updaterOrValue
 }
+
+// Toast function using vue-sonner
+export { toast } from 'vue-sonner'