Controller-First Black Screen + One-Time Auth (Steam Deck Gaming Mode)

Experimental fork build based on upstream v0.3.1 with two additions:

• Controller-first black screen (Fyne path): Main-menu black screen stays in Fyne, avoids forcing SDL input window for this flow.
• One-time auth improvement: After first successful Start USB auth, subsequent runs no longer reprompt (including across restarts, if rule scope still matches).

Tested in Steam Deck Gaming Mode (Non-Steam app launch), controller-first workflow.