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

e2e/specs/channels/own-meta-app.spec.ts

@@ -13,7 +13,7 @@ import {
 // by the dashboard's unit tests.
 
 test.describe('a number or Page from the customer\'s own Meta app', () => {
-  test('a WhatsApp number receives messages: its webhooks are pointed at ChatterMate on connect @channels', async ({ agent, llm, adminApi, request }) => {
+  test('a WhatsApp number receives messages: its webhooks are pointed at ReplyPier on connect @channels', async ({ agent, llm, adminApi, request }) => {
     await llm.script(agent, (s) => s
       .when(/opening hours/i).reply('We are open 9am to 5pm, Monday to Friday.')
       .otherwise().reply('Happy to help!'))