Add packages/common for shared utilities

Create new @reviq/common package with environment-agnostic utilities:
- Date formatting: formatDate, formatDateTime, formatLongDate,
  formatRelativeDate, formatRelativeTime
- User utilities: getUserInitials, formatRole

Consolidate date formatting from publisher-dashboard into shared package.
All utilities include comprehensive test coverage with bun:test.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

packages/common/src/user.ts

@@ -0,0 +1,51 @@
+/**
+ * User-related utility functions
+ */
+
+interface UserLike {
+  displayName?: string | null;
+  email: string;
+}
+
+/**
+ * Generate initials from a user's display name or email.
+ * - For display names with 2+ words: first and last initials (e.g., "John Doe" -> "JD")
+ * - For single word names: first 2 characters (e.g., "John" -> "JO")
+ * - Falls back to first 2 characters of email if no display name
+ * - Returns "??" if user is null/undefined
+ *
+ * @example
+ * getUserInitials({ displayName: "John Doe", email: "john@example.com" }) // "JD"
+ * getUserInitials({ displayName: "John", email: "john@example.com" })     // "JO"
+ * getUserInitials({ email: "john@example.com" })                          // "JO"
+ * getUserInitials(null)                                                   // "??"
+ */
+export function getUserInitials(user: UserLike | null | undefined): string {
+  if (!user) {
+    return "??";
+  }
+
+  if (user.displayName) {
+    const parts = user.displayName.split(" ");
+    const firstPart = parts[0];
+    const lastPart = parts[parts.length - 1];
+    if (parts.length >= 2 && firstPart && lastPart) {
+      return (firstPart.charAt(0) + lastPart.charAt(0)).toUpperCase();
+    }
+    return user.displayName.slice(0, 2).toUpperCase();
+  }
+
+  return user.email.slice(0, 2).toUpperCase();
+}
+
+/**
+ * Format a role string for display (capitalizes first letter).
+ *
+ * @example
+ * formatRole("admin")  // "Admin"
+ * formatRole("member") // "Member"
+ * formatRole("owner")  // "Owner"
+ */
+export function formatRole(role: string): string {
+  return role.charAt(0).toUpperCase() + role.slice(1);
+}