Download Manager Implementation

[YoganshSharma]

Tasks/Requirements

• Create download list page UI (Svelte components)
• Implement queue management logic (Rust backend)
• Add progress tracking and real-time UI updates
• Implement pause/resume/cancel functionality
• Add download history storage
• Create notification integration
  • Depends on: Add Desktop Notifications #15
• Add configuration options (concurrent limits, speed limits)
  • Depends on: Save settings in a readable config file (preferably toml) #20