Implement Core Functionality of BitCell Wallet

[Steake]

Develop initial wallet features starting from the Blockchain-p2p-networking branch:

• Modular Rust components for wallet creation, seed phrase management, address generation/management, transaction handling, balance display, history
• Slint UI for desktop/mobile
• Initial support: Bitcoin, Ethereum, custom blockchains
• Codebase maintainable, modular, performance-centric
• Smallest memory footprint possible
  Assignee: app/copilot-swe-agent
  Label: enhancement