fix(desktop): harden startup and connection feedback

[KillerQueen-Z]

Summary

• replace the initial white window with a branded startup screen
• wait for the renderer first paint before revealing the main window
• show a retryable failure screen when the agent or renderer cannot start
• add single-instance focus behavior and trusted startup IPC checks
• distinguish connecting, reconnecting, loading-wallet, and unavailable states
• version the desktop beta as 0.1.3-beta.1

Validation

• desktop typecheck, lint, production build, and macOS packaging passed
• three Finder cold-start cycles passed with wallet recovery
• repeat-open kept one window and one backend
• exact 0.1.3-beta.1 clean-package launch passed
• no new macOS crash reports were generated

Release artifact

• Franklin-0.1.3-beta.1-arm64.dmg
• SHA-256: 4595c3583292c8802e024ace8522d15034985bdc9f9cfbfe5fab41bed37ad605

This remains an unsigned, non-notarized beta.