[never-seek]

Why

China-region generation used a fixed en-us locale even though the current China iCloud web application uses zh-cn. In addition, pasted JavaScript bundles were accepted as cookie text and then failed later with an unhelpful authentication error.

What changed

• Made Hide My Email generation locale region-specific (zh-cn for China and en-us globally).
• Reject non-cookie JavaScript snippets before they are sent as a Cookie header.
• Added regression tests for locale selection and invalid input handling.

Verification

• testDebugUnitTest
• assembleDebug
• Manual Android verification (no connected emulator/device)

Checklist

• I kept this PR focused and updated relevant documentation.
• I did not include cookies, credentials, Apple IDs, real aliases, signing keys, or personal logs.
• I agree to license this contribution under the repository's MIT License.