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

CONTRIBUTING.md

@@ -1,11 +1,11 @@
-# Contributing to ChatterMate
+# Contributing to ReplyPier
 
 Thanks for your interest in contributing! This document explains how to get
 your changes accepted.
 
 ## License
 
-The ChatterMate open-source core is licensed under the
+The ReplyPier open-source core is licensed under the
 [Apache License 2.0](LICENSE). By contributing, you agree that your
 contributions will be licensed under Apache-2.0.