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/tests/agents/test_guardrail_policy.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.
@@ -283,7 +283,7 @@ class TestRefusalDetection:
         "I can only assist with questions related to freetest. How can I help?",
         "I can only help with questions about Acme — what do you need?",
         "Sorry, I can only assist with inquiries about our products.",
-        "I can only help with ChatterMate topics.",
+        "I can only help with ReplyPier topics.",
     ])
     def test_recognises_decline_variants(self, reply):
         assert looks_like_scope_refusal(reply) is True