feat(schema-manager): Add Schema Management module and expose it in public API; update README to mark Phase 3 complete and move priorities to Phase 4

ts/domain/schema/index.ts

@@ -0,0 +1,26 @@
+/**
+ * Schema Management Module
+ *
+ * Index mapping management, templates, and migrations
+ */
+
+// Main classes
+export { SchemaManager, createSchemaManager } from './schema-manager.js';
+
+// Types
+export type {
+  FieldType,
+  FieldDefinition,
+  IndexSettings,
+  IndexMapping,
+  IndexSchema,
+  SchemaMigration,
+  MigrationStatus,
+  MigrationHistoryEntry,
+  SchemaManagerConfig,
+  SchemaValidationResult,
+  SchemaDiff,
+  IndexTemplate,
+  ComponentTemplate,
+  SchemaManagerStats,
+} from './types.js';