chore(brand): rename the product to ReplyPier

The upstream project name is gone from code, assets, docs and build
output: brand strings, domains (replypier.site and its app/api/docs/help
subdomains), env prefixes, image and network names, the widget's public
JS API (window.ReplyPier, replypierId/BaseUrl/Config/Token), CSS tokens
(--rp-*), file and directory names, and the WordPress plugin package.

- widget loader is now webclient/replypier.min.js; both bundles rebuilt
  from source (backend/assets/widget.{js,css}, frontend/public/webclient)
- NOTICE, llms.txt, CONTRIBUTING, HELP_CENTER_INFRA and config.dev.js
  rewritten rather than string-swapped; the demo config no longer ships
  the previous vendor's Firebase/Razorpay/Google keys
- new migration replypier_ai_model_001 adds REPLYPIER to the managed
  AIModelType and rewrites pre-rename rows
- local compose project, database, role and volume renamed; LOCAL_DEPLOY
  documents carrying the old local data over

NOTICE

@@ -1,8 +1,9 @@
-ChatterMate
-Copyright 2024-2026 ChatterMate
+ReplyPier
+Copyright 2024-2026 ReplyPier
 
-This product includes software developed by ChatterMate
-(https://chattermate.chat).
+This product is the ReplyPier AI customer-support platform: an AI agent answers
+first from your own knowledge base, a human takes over in the same conversation,
+and the visitor can rate the service at the end.
 
-Licensed under the Apache License, Version 2.0. See the LICENSE file for
-the full license text.
+Licensed under the Apache License, Version 2.0. See the LICENSE file for the
+full license text. Contribution terms are in CONTRIBUTING.md.