browser: add vx6 transfer dashboard and history support

[sapphire-2112]

Summary

Adds a new vx6://transfers dashboard page for transfer visibility and browser-side transfer history support.

Features

• added vx6://transfers route
• added homepage and side-navigation integration
• added browser-side sent transfer history persistence
• added transfer status and timestamp visualization
• added grouped receive-transfer visualization support
• improved transfer observability inside the Qt browser shell

Notes

• sent transfer history is stored locally in a browser-managed history log
• receive visualization currently depends on sender-grouped receive directories ending in _vx6
• receive-group visualization and runtime receive-path validation are still under active testing
• browser-side changes only; no VX6 protocol/core behavior changed