feat(shared-stores): add generic data export/import utilities

exportToJSON, exportToCSV (with BOM for Excel), importFromJSON,
downloadFile, timestampedFilename. Works with any Dexie table.
Supports filtering, column selection, custom formatters, ID
regeneration, and transform functions. 16 tests.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/shared-stores/src/data-export.ts

@@ -0,0 +1,151 @@
+/**
+ * Data Export/Import Utilities
+ *
+ * Generic functions for exporting IndexedDB data to JSON/CSV
+ * and importing from JSON. Works with any Dexie table.
+ *
+ * @example
+ * ```typescript
+ * import { exportToJSON, exportToCSV, importFromJSON, downloadFile } from '@manacore/shared-stores';
+ * import { db } from '$lib/data/database';
+ *
+ * // Export contacts as JSON
+ * const data = await exportToJSON(db.table('contacts'));
+ * downloadFile(data, 'contacts.json', 'application/json');
+ *
+ * // Export time entries as CSV
+ * const csv = await exportToCSV(db.table('timeEntries'), {
+ *   columns: ['date', 'description', 'duration'],
+ *   headers: ['Datum', 'Beschreibung', 'Dauer'],
+ * });
+ * downloadFile(csv, 'entries.csv', 'text/csv');
+ *
+ * // Import from JSON file
+ * const file = inputElement.files[0];
+ * const count = await importFromJSON(db.table('contacts'), file);
+ * ```
+ */
+
+import type { Table } from 'dexie';
+
+// ─── Export to JSON ───────────────────────────────────────
+
+export interface ExportJSONOptions {
+	/** Filter records before export (e.g., exclude deleted) */
+	filter?: (record: Record<string, unknown>) => boolean;
+	/** Pretty-print with indentation (default: true) */
+	pretty?: boolean;
+}
+
+/** Export all records from a Dexie table as a JSON string. */
+export async function exportToJSON(table: Table, options?: ExportJSONOptions): Promise<string> {
+	let records = await table.toArray();
+	if (options?.filter) {
+		records = records.filter(options.filter);
+	}
+	return JSON.stringify(records, null, options?.pretty !== false ? 2 : undefined);
+}
+
+// ─── Export to CSV ────────────────────────────────────────
+
+export interface ExportCSVOptions {
+	/** Column keys to include (default: all keys from first record) */
+	columns?: string[];
+	/** Display headers (default: same as columns) */
+	headers?: string[];
+	/** Filter records before export */
+	filter?: (record: Record<string, unknown>) => boolean;
+	/** Column separator (default: ';' for Excel compat) */
+	separator?: string;
+	/** Format a cell value (default: auto-quote strings with separator) */
+	formatCell?: (value: unknown, key: string) => string;
+}
+
+/** Export all records from a Dexie table as a CSV string. */
+export async function exportToCSV(table: Table, options?: ExportCSVOptions): Promise<string> {
+	let records: Record<string, unknown>[] = await table.toArray();
+	if (options?.filter) {
+		records = records.filter(options.filter);
+	}
+	if (records.length === 0) return '';
+
+	const sep = options?.separator ?? ';';
+	const columns = options?.columns ?? Object.keys(records[0]);
+	const headers = options?.headers ?? columns;
+
+	const formatCell =
+		options?.formatCell ??
+		((value: unknown, _key: string) => {
+			if (value === null || value === undefined) return '';
+			const str = String(value);
+			if (str.includes(sep) || str.includes('"') || str.includes('\n')) {
+				return `"${str.replace(/"/g, '""')}"`;
+			}
+			return str;
+		});
+
+	const rows = records.map((record) =>
+		columns.map((col) => formatCell(record[col], col)).join(sep)
+	);
+
+	const BOM = '\uFEFF'; // UTF-8 BOM for Excel compatibility
+	return BOM + [headers.join(sep), ...rows].join('\n');
+}
+
+// ─── Import from JSON ─────────────────────────────────────
+
+export interface ImportJSONOptions {
+	/** Transform each record before inserting */
+	transform?: (record: Record<string, unknown>) => Record<string, unknown>;
+	/** Generate new IDs for imported records (default: true) */
+	newIds?: boolean;
+	/** Clear table before import (default: false) */
+	clearFirst?: boolean;
+}
+
+/** Import records from a JSON file into a Dexie table. Returns count of imported records. */
+export async function importFromJSON(
+	table: Table,
+	file: File,
+	options?: ImportJSONOptions
+): Promise<number> {
+	const text = await file.text();
+	let records: Record<string, unknown>[] = JSON.parse(text);
+
+	if (!Array.isArray(records)) {
+		throw new Error('JSON must contain an array of records');
+	}
+
+	if (options?.transform) {
+		records = records.map(options.transform);
+	}
+
+	if (options?.newIds !== false) {
+		records = records.map((r) => ({ ...r, id: crypto.randomUUID() }));
+	}
+
+	if (options?.clearFirst) {
+		await table.clear();
+	}
+
+	await table.bulkAdd(records);
+	return records.length;
+}
+
+// ─── File Download Trigger ────────────────────────────────
+
+/** Trigger a browser file download from a string. */
+export function downloadFile(content: string, filename: string, mimeType: string): void {
+	const blob = new Blob([content], { type: `${mimeType};charset=utf-8` });
+	const url = URL.createObjectURL(blob);
+	const a = document.createElement('a');
+	a.href = url;
+	a.download = filename;
+	a.click();
+	URL.revokeObjectURL(url);
+}
+
+/** Generate a timestamped filename. */
+export function timestampedFilename(prefix: string, ext: string): string {
+	return `${prefix}-${new Date().toISOString().split('T')[0]}.${ext}`;
+}