refactor(messaging): drop bespoke messenger/inbox/mail + wrapper page headers

Delete the now-dead pre-SDK stack (messenger/inbox/mail components + their
*-api libs + messenger-socket) — both tabs render the @insignia/iios-messaging-ui
SDK. Remove the redundant <PageHead> from the messenger/inbox SDK wrappers (the
Topbar already shows the title); the SDK itself renders no header.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/components/dashboard/inbox-sdk.tsx

@@ -12,19 +12,12 @@ import "@insignia/iios-messaging-ui/styles.css";
 import { isShellConfigured } from "@/lib/appshell";
 import { CrmInboxAdapter } from "@/lib/crm-inbox-adapter";
 import type { DataDoor } from "@/lib/crm-messaging-adapter";
-import { PageHead } from "./ui";
 
 const SHELL = isShellConfigured();
 
 export function InboxSdk() {
   return (
     <div className="view">
-      <PageHead
-        eyebrow="Communication"
-        title="Inbox"
-        subtitle="Mentions, messages, alerts and mail — all in one, via the messaging SDK"
-        icon="bell"
-      />
       {!SHELL && (
         <div style={{ margin: "0 0 14px", padding: "8px 14px", borderRadius: 10, background: "var(--panel-2)", color: "var(--muted)", fontSize: 13, border: "1px solid var(--border)" }}>
           Demo mode — running on the SDK&apos;s mock inbox adapter.