fix: Improve error handling and remove Tauri dependencies

- Replace expect() with proper error handling in main.rs (tokio runtime)
- Replace nested expect() with match statements in app.rs (AppState fallback)
- Add better error messages and graceful error handling
- Update dependencies (reqwest 0.12.28, tokio 1.48.0)
- Fix Makefile: Replace bitvault-ui references with bitvault-app
- Fix Dockerfile: Remove Tauri/trunk dependencies (using egui/eframe, not Tauri)
- Update Cargo.lock with latest dependency versions

Note: Vulnerabilities in bitvault-ui are from a different project.
This project uses egui/eframe, not Tauri.

Author: secsovereign