Sender avatars, PDF password preview, contacts autosave, account-view + Trash/Spam auto-purge, UI polish

Sender avatars (privacy-safe, server-fetched, cached):
- New GET /api/avatar resolves Gravatar (d=404) then the sender domain's favicon
  under the SSRF guard, Redis-cached (hit+miss); gated by SENDER_AVATARS_ENABLED.
  GuardedResponse gains raw bytes. Shown in the mail list, reading pane, People
  panel, and Contacts (overlay that falls back to initials on a miss).

PDF preview:
- Password-protected PDFs now prompt in-place and retry (pdf.js PasswordException),
  with a clear error for other load failures instead of a blank overlay. The
  password is remembered per attachment until the thread is left; clicking the
  field no longer dismisses the overlay.

Contacts:
- Autosave reply recipients: message.sent now carries to/cc (name+email); the
  contacts plugin subscribes and adds any non-contact recipients to the Autosaved
  group. Contact avatars show the gravatar/favicon via /api/avatar.

Mail views / retention:
- Clicking an account shows all its mail except Trash/Spam (was inbox-only).
- Daily cron autopurge_trash_spam permanently deletes Trash/Spam older than
  TRASH_RETENTION_DAYS (default 30; 0 disables) — server EXPUNGE + local rows.

UI polish:
- Ultimo signet logo in the Mail/Calendar/Contacts sidebar header and collapsed
  rail; consistent 11px top margin and vertically-aligned header row across states
  (fixed-size flex icon buttons); SVG favicon on the browser tab.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01U72FZiF1W1pb8XxyWBTREA

frontend/src/components/list/MessageList.tsx

@@ -7,6 +7,7 @@ import { api } from "../../lib/api";
 import { formatClock, getDateLocale } from "../../lib/timeFormat";
 import type { Address, ThreadSummary } from "../../lib/types";
 import { Icon } from "../Icon";
+import { AvatarImage } from "../SenderAvatar";
 import { LabelChips } from "../mail/LabelChips";
 
 function timeLabel(iso: string): string {
@@ -165,10 +166,11 @@ export function MessageList({
                   )}
                   <div className={checkMode ? "hidden" : "contents group-hover/av:hidden"}>
                     <span
-                      className="flex h-[33px] w-[33px] items-center justify-center rounded-full text-[13px] font-semibold text-white"
+                      className="relative flex h-[33px] w-[33px] items-center justify-center overflow-hidden rounded-full text-[13px] font-semibold text-white"
                       style={{ backgroundColor: avatarBg }}
                     >
                       {initials(primary)}
+                      <AvatarImage email={primary?.email} />
                     </span>
                     {extra > 0 && (
                       <span className="absolute -bottom-1 -left-1.5 rounded-full bg-app-hover px-1 text-[10px] font-medium text-app-muted ring-2 ring-app-surface">