feat(phase3): import/export, sparklines, user theme overrides

- JSON import/export with conflict resolution (skip/overwrite) + admin UI
- Ping history sparklines on AppWidget and AppCard (24h, 288 points)
- Hourly cleanup job for old AppStatus records
- User theme preferences (hue, saturation, mode, background, locale)
- Settings page with ThemeCustomizer (sliders, toggles, live preview)
- Prisma migration for user preference fields
- i18n translations for all new strings (EN/RU)

src/lib/stores/theme.svelte.ts

@@ -118,6 +118,30 @@ class ThemeStore {
 		this.primaryHue = Math.max(0, Math.min(360, hue));
 		this.primarySaturation = Math.max(0, Math.min(100, saturation));
 	}
+
+	/**
+	 * Apply non-null server-stored user preferences over localStorage defaults.
+	 * Call from +layout.svelte when user data is available.
+	 */
+	loadFromServer(prefs: {
+		themeMode?: string | null;
+		primaryHue?: number | null;
+		primarySaturation?: number | null;
+		backgroundType?: string | null;
+	}) {
+		if (prefs.themeMode != null) {
+			this.mode = prefs.themeMode as ThemeMode;
+		}
+		if (prefs.primaryHue != null) {
+			this.primaryHue = prefs.primaryHue;
+		}
+		if (prefs.primarySaturation != null) {
+			this.primarySaturation = prefs.primarySaturation;
+		}
+		if (prefs.backgroundType != null) {
+			this.backgroundType = prefs.backgroundType as BackgroundType;
+		}
+	}
 }
 
 export const theme = new ThemeStore();