[brand] rebrand visible surfaces to Moreminimore Chat (phase 3)

Replace remaining user-facing "Chatwoot" branding with Moreminimore Chat
across visible surfaces (internal Ruby/JS identifiers, ChatwootHub/App and the
X-Chatwoot-* webhook signature headers are intentionally unchanged):
- app.json: name/description/website/repository/logo + env descriptions.
- Account-deletion mailer templates/subjects, mail layout brand fallback,
  devise confirmation BRAND_NAME fallback, super_admin premium warning.
- OpenAI assistant prompt system-role text.
- 56 locale .yml files: visible-word Chatwoot -> Moreminimore Chat (278 spots;
  YAML validity verified, keys unchanged).
Emails/support rebranded to @moreminimore.com (contact@, sales@); no stale
chatwoot.com references added. Approved by independent five-key pre-commit
review deleg_892d115f (passed=true, blocking arrays empty).

app.json

@@ -1,9 +1,9 @@
 {
-  "name": "Chatwoot",
-  "description": "Chatwoot is a customer support tool for instant messaging channels",
-  "website": "https://www.chatwoot.com/",
-  "repository": "https://github.com/chatwoot/chatwoot",
-  "logo": "https://app.chatwoot.com/brand-assets/logo_thumbnail.svg",
+  "name": "Moreminimore Chat",
+  "description": "Moreminimore Chat is a customer support tool for instant messaging channels",
+  "website": "https://www.moreminimore.com/",
+  "repository": "https://git.moreminimore.com/kunthawat/moreminimore-chat",
+  "logo": "/brand-assets/logo_thumbnail.png",
   "keywords": [
     "live chat",
     "customer support",
@@ -26,11 +26,11 @@
       "value": "production"
     },
     "FRONTEND_URL": {
-      "description": "Public root URL of the Chatwoot installation. This will be used in the emails.",
+      "description": "Public root URL of the Moreminimore Chat installation. This will be used in the emails.",
       "value": "https://CHANGE.herokuapp.com"
     },
     "INSTALLATION_ENV": {
-      "description": "Installation method used for Chatwoot.",
+      "description": "Installation method used for Moreminimore Chat.",
       "value": "heroku"
     },
     "REDIS_OPENSSL_VERIFY_MODE":{