Persist authenticated Remote name updates

[enaboapps]

Summary

• accept optional authenticated deviceName metadata on protocol v1 pings
• validate and persist the paired Remote display name on Windows and macOS
• return a sanitized non-fatal sync error and roll back conditionally when persistence fails
• preserve legacy empty pings and existing pairing identity

Validation

• npm run lint
• npm test (73 tests passed)
• npm run build
• cargo fmt --manifest-path src-tauri/Cargo.toml --check
• cargo clippy --manifest-path src-tauri/Cargo.toml --all-targets -- -D warnings
• cargo test --manifest-path src-tauri/Cargo.toml (210 unit tests and 2 config tests passed)
• npm run tauri build -- --no-bundle
• Physical Windows/macOS pairing checks remain to be recorded

Counterpart

• Add a customizable Remote device name switchify-remote#71

Closes #639

[enaboapps]

Independent latest-head review completed at 393e220f68a7e930d0a2add342aa4295c0177613. Three initial findings were fixed across the linked PRs; repeat review found no actionable issues. Frontend, Windows, and macOS checks are green.