Refine settings and panel preferences

docs/PLAN.md

@@ -31,3 +31,4 @@ Updated: 2026-04-02
 15. Added editable System settings with shared validation, a system update API, service/port conflict protection, and UI coverage for local save flows.
 16. Simplified the System tab layout by removing the redundant Runtime card and collapsing those fields into a compact settings section.
 17. Moved panel auth to server-issued expiring tokens with `sessionStorage` persistence and Compose-configurable credentials/TTL.
+18. Reworked Settings to store panel language/theme in `localStorage`, added RU/EN UI switching, and made service deletion warn before cascading linked-user removal.

docs/PROJECT_INDEX.md

@@ -29,6 +29,8 @@ Updated: 2026-04-02
 - `src/app.css`: full panel styling
 - `src/data/mockDashboard.ts`: default panel state and frontend fallback snapshot
 - `src/lib/3proxy.ts`: formatting and status helpers
+- `src/lib/panelPreferences.ts`: client-side `localStorage` preferences and theme application helpers
+- `src/lib/panelText.ts`: EN/RU panel copy and labels for translated UI chrome
 - `src/lib/3proxy.test.ts`: paranoia-oriented tests for core domain rules
 - `src/shared/contracts.ts`: shared panel, service, user, and API data contracts
 - `src/shared/validation.ts`: shared validation for user creation, system edits, protocol mapping, and quota conversion