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/string.ts

@@ -0,0 +1,43 @@
+/**
+ * String utility functions
+ */
+
+/**
+ * Truncate a string to a maximum length with ellipsis
+ */
+export function truncate(str: string, maxLength: number): string {
+  if (str.length <= maxLength) return str;
+  return str.slice(0, maxLength - 3) + '...';
+}
+
+/**
+ * Capitalize the first letter of a string
+ */
+export function capitalize(str: string): string {
+  if (!str) return str;
+  return str.charAt(0).toUpperCase() + str.slice(1);
+}
+
+/**
+ * Generate a random string ID
+ */
+export function generateId(length: number = 8): string {
+  const chars = 'abcdefghijklmnopqrstuvwxyz0123456789';
+  let result = '';
+  for (let i = 0; i < length; i++) {
+    result += chars.charAt(Math.floor(Math.random() * chars.length));
+  }
+  return result;
+}
+
+/**
+ * Slugify a string for URLs
+ */
+export function slugify(str: string): string {
+  return str
+    .toLowerCase()
+    .trim()
+    .replace(/[^\w\s-]/g, '')
+    .replace(/[\s_-]+/g, '-')
+    .replace(/^-+|-+$/g, '');
+}