do to formatters

apps/website/lib/contracts/formatters/Formatter.ts

@@ -0,0 +1,22 @@
+/**
+ * Formatter contract
+ * 
+ * Deterministic, reusable, UI-only formatting/mapping logic.
+ * 
+ * Based on DISPLAY_OBJECTS.md:
+ * - Class-based
+ * - Immutable
+ * - Deterministic
+ * - Side-effect free
+ * - No Intl.* or toLocale*
+ * - No business rules
+ */
+
+export interface Formatter {
+  /**
+   * Format or map the display object
+   * 
+   * @returns Primitive values only (strings, numbers, booleans)
+   */
+  format(): unknown;
+}