[15] Settings: themes, i18n (pt-BR / en-US) and persisted defaults

[jvwaldrich0]

Task 15 of 16 — these are sequential, do them in order.

Previous: #17 · Next: #19

Port target: cloudpark-toolkit (Go) → this repo (Rust). Reference paths below are relative to that repo.

Goal

Settings: theme picker, language, and persisted defaults.

Scope

• Settings overlay on esc at the index root.
• Themes: the palette list from task 03 (Default, Matrix, Ocean, Mono, Dracula, Gruvbox, Nord, Sunset, Forest, Rose), applied live to every screen.
• Language: pt-br (default) and en-us. Translation keys are the English source strings, so en-us needs no table — t() falls back to the key.
• Persisted defaults: ticket dir, printer port + baud, barcode delay, HW address. Store as TOML at $XDG_CONFIG_HOME/virtusdev/config.toml (fall back to ~/.config). Launch forms prefill from it.
• First run: open the defaults editor once, esc skips.

Reference

cloudpark-toolkit/internal/tui/settings.go, config.go, i18n.go, theme.go

Done when

• Theme and language changes persist across restarts.
• A missing or corrupt config file falls back to defaults instead of failing to start.
• Every user-facing string on the emulator screens goes through t().