Release v0.1.20

[odrasile]

Summary

• Add provider state-machine groundwork and documentation for Claude/Gemini usage states.
• Standardize widget fallback status messages and add provider log copy support.
• Bump app version to 0.1.20 and keep generated Tauri resources out of git.

Validation

• npm test
• npm run build
• cargo fmt --manifest-path src-tauri/Cargo.toml --check
• cargo check --manifest-path src-tauri/Cargo.toml
• npm run tauri:build

[odrasile]

Superseded by release/v0.1.21, which includes v0.1.20 changes plus the tested X11 workspace fix and has successful release installers for Ubuntu, Windows, and macOS.