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.test.ts

@@ -0,0 +1,84 @@
+import { describe, expect, test } from "bun:test";
+import { formatRole, getUserInitials } from "./user.js";
+
+describe("getUserInitials", () => {
+  test("returns '??' for null", () => {
+    expect(getUserInitials(null)).toBe("??");
+  });
+
+  test("returns '??' for undefined", () => {
+    expect(getUserInitials(undefined)).toBe("??");
+  });
+
+  test("returns initials from display name with two words", () => {
+    expect(
+      getUserInitials({ displayName: "John Doe", email: "john@example.com" }),
+    ).toBe("JD");
+  });
+
+  test("returns initials from display name with multiple words", () => {
+    expect(
+      getUserInitials({
+        displayName: "John Michael Doe",
+        email: "john@example.com",
+      }),
+    ).toBe("JD");
+  });
+
+  test("returns first two characters for single word display name", () => {
+    expect(
+      getUserInitials({ displayName: "John", email: "john@example.com" }),
+    ).toBe("JO");
+  });
+
+  test("returns uppercase initials", () => {
+    expect(
+      getUserInitials({
+        displayName: "john doe",
+        email: "john@example.com",
+      }),
+    ).toBe("JD");
+  });
+
+  test("falls back to email when no display name", () => {
+    expect(getUserInitials({ email: "john@example.com" })).toBe("JO");
+  });
+
+  test("handles null display name", () => {
+    expect(
+      getUserInitials({ displayName: null, email: "alice@example.com" }),
+    ).toBe("AL");
+  });
+
+  test("handles empty display name", () => {
+    expect(
+      getUserInitials({ displayName: "", email: "bob@example.com" }),
+    ).toBe("BO");
+  });
+});
+
+describe("formatRole", () => {
+  test("capitalizes 'admin'", () => {
+    expect(formatRole("admin")).toBe("Admin");
+  });
+
+  test("capitalizes 'member'", () => {
+    expect(formatRole("member")).toBe("Member");
+  });
+
+  test("capitalizes 'owner'", () => {
+    expect(formatRole("owner")).toBe("Owner");
+  });
+
+  test("handles already capitalized roles", () => {
+    expect(formatRole("Admin")).toBe("Admin");
+  });
+
+  test("handles single character", () => {
+    expect(formatRole("a")).toBe("A");
+  });
+
+  test("handles empty string", () => {
+    expect(formatRole("")).toBe("");
+  });
+});