feat(user-preferences): implement user preferences management with backend support

Added functionality for managing user preferences, including the ability to update preferences via a new API endpoint. The preferences are now stored server-side, allowing for synchronization across devices. Updated relevant components to handle user preferences, including the UserMenu and settings views. Enhanced internationalization support for error messages related to preference updates.

migrations/sqlite/000000_init.up.sql

@@ -222,6 +222,10 @@ CREATE TABLE IF NOT EXISTS users (
     tenant_id INTEGER,
     is_active BOOLEAN NOT NULL DEFAULT 1,
     can_access_all_tenants BOOLEAN NOT NULL DEFAULT 0,
+    -- Per-user JSON preferences (memory toggle, future UI knobs).
+    -- SQLite has no JSONB; store as TEXT and let GORM (de)serialise via
+    -- the driver.Valuer / sql.Scanner methods on types.UserPreferences.
+    preferences TEXT NOT NULL DEFAULT '{}',
     created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
     updated_at DATETIME DEFAULT CURRENT_TIMESTAMP,
     deleted_at DATETIME