chore: settle product naming across app, widget and deployments

One word everywhere: ReplyPier in UI copy, package and image names, the
replypier.site domains (app/api/docs/help), REPLYPIER_* settings and the
--rp-* design tokens.

- public widget API is window.ReplyPier with replypierId / replypierBaseUrl /
  replypierConfig / replypierToken, loader at webclient/replypier.min.js;
  both bundles rebuilt from source
- NOTICE, llms.txt, CONTRIBUTING, HELP_CENTER_INFRA and the demo runtime
  config rewritten; the demo config ships no third-party keys
- migration adds the ReplyPier managed model value to the AI model enum
- local compose project, database, role, volume and Docker network carry the
  same name

backend/app/services/faq_article_import.py

@@ -1,5 +1,5 @@
 """
-Copyright 2024-2026 ChatterMate
+Copyright 2024-2026 ReplyPier
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -93,7 +93,7 @@ _GENERIC_SECTIONS = frozenset({
 # Internal scheme marking images collected during conversion, replaced with the
 # re-hosted URL afterwards (conversion is sync; storage is async). The trailing
 # ".img" delimits the index so "…//1.img" is never a prefix of "…//10.img".
-_IMG_PLACEHOLDER = "cm-pending-image://{index}.img"
+_IMG_PLACEHOLDER = "rp-pending-image://{index}.img"
 
 
 @dataclass