refactor(features): split entities into models/ + errors/ subdirs

All 5 features (auth, blog, marketing-pages, navigation; media has no
entities yet) now follow Lazar's pattern:
- entities/<x>.ts → entities/models/<x>.ts
- entities/errors.ts → entities/errors/<domain>.ts + errors/common.ts

Updates all import paths across factories, contracts, tests, use cases,
controllers, repositories, integrations, and src/index.ts exports.

navigation divergence: had no errors.ts; errors/header.ts +
errors/common.ts added as new forward-looking stubs.

Refactor log: docs/superpowers/refactor-logs/2026-05-05-lazar-pattern-conformance.md
Spec: §5, §9.3

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/auth/src/entities/errors/auth.ts

@@ -0,0 +1,17 @@
+export class AuthenticationError extends Error {
+  constructor(message: string, options?: ErrorOptions) {
+    super(message, options);
+  }
+}
+
+export class UnauthenticatedError extends Error {
+  constructor(message: string, options?: ErrorOptions) {
+    super(message, options);
+  }
+}
+
+export class UnauthorizedError extends Error {
+  constructor(message: string, options?: ErrorOptions) {
+    super(message, options);
+  }
+}

packages/auth/src/entities/errors/common.ts

@@ -0,0 +1,5 @@
+export class InputParseError extends Error {
+  constructor(message: string, options?: ErrorOptions) {
+    super(message, options);
+  }
+}

packages/auth/src/entities/errors/errors.test.ts

@@ -0,0 +1,39 @@
+import { describe, expect, it } from "vitest";
+import {
+  AuthenticationError,
+  UnauthenticatedError,
+  UnauthorizedError,
+} from "./auth";
+import { InputParseError } from "./common";
+
+describe("AuthenticationError", () => {
+  it("is an instance of Error with the given message", () => {
+    const err = new AuthenticationError("bad credentials");
+    expect(err).toBeInstanceOf(Error);
+    expect(err.message).toBe("bad credentials");
+  });
+});
+
+describe("UnauthenticatedError", () => {
+  it("is an instance of Error with the given message", () => {
+    const err = new UnauthenticatedError("not logged in");
+    expect(err).toBeInstanceOf(Error);
+    expect(err.message).toBe("not logged in");
+  });
+});
+
+describe("UnauthorizedError", () => {
+  it("is an instance of Error with the given message", () => {
+    const err = new UnauthorizedError("forbidden");
+    expect(err).toBeInstanceOf(Error);
+    expect(err.message).toBe("forbidden");
+  });
+});
+
+describe("InputParseError", () => {
+  it("is an instance of Error with the given message", () => {
+    const err = new InputParseError("invalid input");
+    expect(err).toBeInstanceOf(Error);
+    expect(err.message).toBe("invalid input");
+  });
+});