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/index.ts

@@ -0,0 +1,9 @@
+export {
+  formatDate,
+  formatDateTime,
+  formatLongDate,
+  formatRelativeDate,
+  formatRelativeTime,
+  type FormatRelativeDateOptions,
+} from "./format-date.js";
+export { formatRole, getUserInitials } from "./user.js";