fix: persist user settings across sessions

Add userPreferences module to save/load padding, aspect ratio,
export format and quality to localStorage. Applied on mount
in VideoEditor.

Closes #306

src/components/video-editor/VideoEditor.tsx

@@ -21,6 +21,7 @@ import {
 	VideoExporter,
 } from "@/lib/exporter";
 import type { ProjectMedia } from "@/lib/recordingSession";
+import { loadUserPreferences, saveUserPreferences } from "@/lib/userPreferences";
 import { matchesShortcut } from "@/lib/shortcuts";
 import {
 	getAspectRatioValue,

src/lib/userPreferences.ts

@@ -0,0 +1,69 @@
+import type { ExportFormat, ExportQuality } from "@/lib/exporter";
+import type { AspectRatio } from "@/utils/aspectRatioUtils";
+
+const PREFS_KEY = "openscreen_user_preferences";
+
+export interface UserPreferences {
+	/** Default padding % */
+	padding: number;
+	/** Default aspect ratio */
+	aspectRatio: AspectRatio;
+	/** Default export quality */
+	exportQuality: ExportQuality;
+	/** Default export format */
+	exportFormat: ExportFormat;
+}
+
+const DEFAULT_PREFS: UserPreferences = {
+	padding: 50,
+	aspectRatio: "16:9",
+	exportQuality: "good",
+	exportFormat: "mp4",
+};
+
+function safeJsonParse(text: string | null): Record<string, unknown> | null {
+	if (!text) return null;
+	try {
+		return JSON.parse(text);
+	} catch {
+		return null;
+	}
+}
+
+/**
+ * Load persisted user preferences from localStorage.
+ * Returns defaults for any missing or invalid fields.
+ */
+export function loadUserPreferences(): UserPreferences {
+	const raw = safeJsonParse(localStorage.getItem(PREFS_KEY));
+	if (!raw || typeof raw !== "object") return { ...DEFAULT_PREFS };
+
+	return {
+		padding:
+			typeof raw.padding === "number" && Number.isFinite(raw.padding) && raw.padding >= 0 && raw.padding <= 100
+				? raw.padding
+				: DEFAULT_PREFS.padding,
+		aspectRatio:
+			typeof raw.aspectRatio === "string" ? (raw.aspectRatio as AspectRatio) : DEFAULT_PREFS.aspectRatio,
+		exportQuality:
+			raw.exportQuality === "medium" || raw.exportQuality === "source"
+				? (raw.exportQuality as ExportQuality)
+				: DEFAULT_PREFS.exportQuality,
+		exportFormat:
+			raw.exportFormat === "gif" ? (raw.exportFormat as ExportFormat) : DEFAULT_PREFS.exportFormat,
+	};
+}
+
+/**
+ * Persist user preferences to localStorage.
+ * Only the explicitly provided fields are updated.
+ */
+export function saveUserPreferences(partial: Partial<UserPreferences>): void {
+	const current = loadUserPreferences();
+	const merged = { ...current, ...partial };
+	try {
+		localStorage.setItem(PREFS_KEY, JSON.stringify(merged));
+	} catch {
+		// localStorage may be unavailable (e.g. private browsing quota exceeded)
+	}
+}