feat: ChatGPT Custom GPT support in chat bot + sqcp SMTP routing fix

- chat.ts: system prompt now includes step-by-step ChatGPT Custom GPT
  setup (openapi.json import + OAuth), Claude/Cursor/Windsurf config,
  and mortgage broker guidance — bot no longer incorrectly says ChatGPT
  is unsupported
- smtp.ts: all sqcp_* accounts now route to mail.squaremcp.com (SQCP_SMTP_HOST)
  instead of the fetcherpay server
- tools.ts: ACCOUNT_PARAM description now lists all 14 mailboxes including
  the 7 squaremcp.com accounts so Claude picks the right one without guessing
- package.json: postinstall hook runs imapflow patch script after npm install
- hermes-k8s.yaml: updated image digest to current production build

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

hermes-k8s.yaml

@@ -22,7 +22,7 @@ spec:
         fsGroup: 1000
       containers:
         - name: hermes-mcp
-          image: localhost:32000/hermes-mcp@sha256:17f1f7ce059f0f87d9c34c39e2ea0fb1f25cf72f9279341c5912e6c35690f43a
+          image: localhost:32000/hermes-mcp@sha256:54488f625b5a065f3cfb30d9d0afe269dac65aadd8206652d27da034daf1dee4
           imagePullPolicy: Always
           securityContext:
             allowPrivilegeEscalation: false