feat(mobile-h5): add mock auth helpers for login page

Co-authored-by: Cursor <cursoragent@cursor.com>

mobile-h5/utils/validate-credentials.test.mjs

@@ -0,0 +1,8 @@
+import assert from 'node:assert/strict'
+import { validateCredentials } from './validate-credentials.js'
+
+assert.equal(validateCredentials('', 'x').code, 'EMPTY_USERNAME')
+assert.equal(validateCredentials('  ', 'x').code, 'EMPTY_USERNAME')
+assert.equal(validateCredentials('admin', '').code, 'EMPTY_PASSWORD')
+assert.equal(validateCredentials('admin', '111111').ok, true)
+console.log('validate-credentials: all passed')