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/ticket_email.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.
@@ -52,7 +52,7 @@ _TICKET_MSGID_RE = re.compile(r"ticket-([0-9a-f]{32})(?:\.[^@\s>]+)?@", re.I)
 _ROOT_SUFFIX = "root"
 _SUBJECT_TOKEN_RE = re.compile(rf"\[{TICKET_NUMBER_PREFIX}-(\d+)\]", re.I)
 
-DEFAULT_MSGID_DOMAIN = "chattermate.chat"
+DEFAULT_MSGID_DOMAIN = "replypier.site"
 
 
 def _msgid_domain(from_email: Optional[str] = None) -> str: