feat: redesign settings workspace

[kwp-lab]

Summary

• rebuild Settings as a full-height categorized workspace with session routing and first-run setup
• add automatic saving for ordinary preferences plus dedicated ASR, LLM, and AI-template managers
• align Settings selectors with the recording-source control and show selected draft Provider cards immediately
• avoid unnecessary global-shortcut re-registration and document the new ownership and testing model
• bump Nota from 0.8.0 to 0.9.0 and refresh release metadata

Verification

• npm run check
• 111 frontend tests passed
• 120 Rust tests passed; 5 hardware-dependent tests ignored