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

frontend/nginx.conf

@@ -11,7 +11,7 @@ server {
 
     # Enhanced Security headers.
     # This config only ever runs inside the frontend image, i.e. for self-hosted
-    # deployments - app.chattermate.chat serves the SPA from its own reverse proxy
+    # deployments - app.replypier.site serves the SPA from its own reverse proxy
     # and never routes here, so its CSP is set there and is unaffected by this file.
     # The CSP is repeated in every location block below because an add_header inside
     # a location cancels the inherited ones - change one, change all five.