feat(auth): add anthropic api key storage and cli auth

src/auth/anthropic.test.ts

@@ -0,0 +1,50 @@
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
+import { mkdtempSync, statSync } from 'fs';
+import { tmpdir } from 'os';
+import { join } from 'path';
+
+describe('auth/anthropic', () => {
+  const originalHome = process.env.HOME;
+  const originalEnvKey = process.env.ANTHROPIC_API_KEY;
+
+  let homeDir: string;
+
+  beforeEach(() => {
+    homeDir = mkdtempSync(join(tmpdir(), 'flynn-auth-anthropic-'));
+    process.env.HOME = homeDir;
+    delete process.env.ANTHROPIC_API_KEY;
+    vi.resetModules();
+  });
+
+  afterEach(() => {
+    process.env.HOME = originalHome;
+    if (originalEnvKey) {
+      process.env.ANTHROPIC_API_KEY = originalEnvKey;
+    } else {
+      delete process.env.ANTHROPIC_API_KEY;
+    }
+  });
+
+  it('stores, loads, and clears Anthropic API key', async () => {
+    const mod = await import('./anthropic.js');
+
+    expect(mod.loadStoredAnthropicAuth()).toBeNull();
+
+    mod.storeAnthropicAuth('sk-test');
+    expect(mod.loadStoredAnthropicAuth()?.api_key).toBe('sk-test');
+
+    const authFile = join(homeDir, '.config/flynn/auth.json');
+    const mode = statSync(authFile).mode & 0o777;
+    expect(mode).toBe(0o600);
+
+    mod.clearAnthropicAuth();
+    expect(mod.loadStoredAnthropicAuth()).toBeNull();
+  });
+
+  it('getAnthropicApiKey prefers environment variable', async () => {
+    process.env.ANTHROPIC_API_KEY = 'sk-env';
+    const mod = await import('./anthropic.js');
+    expect(mod.getAnthropicApiKey()).toBe('sk-env');
+  });
+});
+