security: fix path validation bypass, CORS restriction, cookie-import path check

- startsWith('/tmp') matched '/tmpevil' — now requires trailing slash
- CORS Access-Control-Allow-Origin changed from * to http://127.0.0.1:<port>
- cookie-import now validates file paths (was missing validateReadPath)
- 3 new tests for prefix collision and cookie-import path traversal

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

browse/test/commands.test.ts

@@ -1495,4 +1495,32 @@ describe('Path traversal prevention', () => {
       try { fs.unlinkSync(tmpFile); } catch {}
     }
   });
+
+  test('screenshot rejects /tmpevil prefix collision', async () => {
+    await handleWriteCommand('goto', [baseUrl + '/basic.html'], bm);
+    try {
+      await handleMetaCommand('screenshot', ['/tmpevil/steal.png'], bm, () => {});
+      expect(true).toBe(false);
+    } catch (err: any) {
+      expect(err.message).toContain('Path must be within');
+    }
+  });
+
+  test('cookie-import rejects path traversal', async () => {
+    try {
+      await handleWriteCommand('cookie-import', ['../../etc/shadow'], bm);
+      expect(true).toBe(false);
+    } catch (err: any) {
+      expect(err.message).toContain('Path traversal');
+    }
+  });
+
+  test('cookie-import rejects absolute path outside safe dirs', async () => {
+    try {
+      await handleWriteCommand('cookie-import', ['/etc/passwd'], bm);
+      expect(true).toBe(false);
+    } catch (err: any) {
+      expect(err.message).toContain('Path must be within');
+    }
+  });
 });