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

frontend/index.html

@@ -19,7 +19,7 @@
        and src/config/themeColors.ts — a static document cannot import them. */
     (function () {
       try {
-        var stored = localStorage.getItem('cm-theme') || 'light';
+        var stored = localStorage.getItem('rp-theme') || 'light';
         var resolved = stored === 'system'
           ? (window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light')
           : (stored === 'light' ? 'light' : 'dark');