feat: add monorepo configuration and shared packages structure

Root-level setup:
- package.json with Turborepo scripts
- pnpm-workspace.yaml for workspace management
- turbo.json for build pipeline
- Common config files (.nvmrc, .prettierrc, .editorconfig)

Shared packages (packages/):
- @manacore/shared-types - Common TypeScript types
- @manacore/shared-supabase - Unified Supabase client
- @manacore/shared-utils - Date, string, async utilities
- @manacore/shared-ui - React Native UI components (placeholder)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

packages/shared-utils/src/date.ts

@@ -0,0 +1,43 @@
+/**
+ * Date utility functions
+ */
+
+import { format, formatDistanceToNow, parseISO } from 'date-fns';
+import { de, enUS } from 'date-fns/locale';
+
+const locales = {
+  de,
+  en: enUS,
+};
+
+type LocaleKey = keyof typeof locales;
+
+/**
+ * Format a date string to a readable format
+ */
+export function formatDate(
+  date: string | Date,
+  formatStr: string = 'PPP',
+  locale: LocaleKey = 'de'
+): string {
+  const dateObj = typeof date === 'string' ? parseISO(date) : date;
+  return format(dateObj, formatStr, { locale: locales[locale] });
+}
+
+/**
+ * Get relative time from now (e.g., "2 hours ago")
+ */
+export function formatRelativeTime(date: string | Date, locale: LocaleKey = 'de'): string {
+  const dateObj = typeof date === 'string' ? parseISO(date) : date;
+  return formatDistanceToNow(dateObj, {
+    addSuffix: true,
+    locale: locales[locale],
+  });
+}
+
+/**
+ * Format a date for API requests (ISO string)
+ */
+export function toISOString(date: Date): string {
+  return date.toISOString();
+}