WATranslate UI + Chat Management v4.0

CHANGES
1. Visible application name changed to:
   WATranslate

2. Contact avatars added:
   - round WhatsApp-style avatar circles
   - uses first letter of contact display name
   - falls back to final digits of WhatsApp ID

   NOTE:
   These are local UI avatars. WhatsApp Cloud API does not provide the
   customer's WhatsApp profile photo through this implementation.

3. Chat management added:
   - three-dot menu for every chat
   - Archive chat
   - Restore chat
   - Delete chat
   - Archived chats view
   - New incoming message automatically restores an archived chat to Chats

DELETE BEHAVIOR
Delete chat permanently removes that contact's stored messages and contact
record from the WATranslate database.

If that WhatsApp number sends a new message later, WATranslate can create a
new conversation for it again.

IMPORTANT DATABASE STEP
Before uploading the PHP/JS files, run database-v4.0.sql once in phpMyAdmin.

SQL:
ALTER TABLE wa_contacts
ADD COLUMN is_archived TINYINT(1) NOT NULL DEFAULT 0;

INSTALL
1. Back up the current WATranslate folder and database.

2. In phpMyAdmin, select the WATranslate database.

3. Open SQL.

4. Run the SQL from database-v4.0.sql.

5. Upload this ZIP to:
   public_html/whatsapp-server-translator/

6. Extract and overwrite.

FILES OVERWRITTEN:
   public/api.php
   public/webhook.php
   public/index.php
   assets/app.js
   public/assets/app.js

FILES ADDED:
   assets/ui-v4.css
   public/assets/ui-v4.css
   database-v4.0.sql

DO NOT OVERWRITE THE ROOT API WRAPPER
The root file:

public_html/whatsapp-server-translator/api.php

must still contain:

<?php
declare(strict_types=1);
require __DIR__ . '/public/api.php';

NO CHANGES REQUIRED TO
- config.php
- Google API key
- Meta access token
- Meta webhook configuration
- WhatsApp phone number ID
- src/GoogleTranslator.php
- src/WhatsAppCloud.php

AFTER INSTALLATION
Hard refresh:
Cmd + Shift + R

Then test:
- contact avatars appear
- click ⋮ next to a chat
- Archive chat
- open Archived chats
- Restore chat
- Delete a disposable TEST chat only
