Gmail label sync + no-dup backfill, live label/UI updates, account-delete cleanup, Sync-SPAM toggle, sidebar logo

Gmail sync (SPEC: Gmail sync):
- Provider fetches X-GM-LABELS when X-GM-EXT-1 is advertised; parses custom labels
  (system labels dropped, mUTF-7 decoded) onto RemoteMessage.
- Engine syncs only system folders + All Mail for Gmail, skips every label folder,
  and dedupes the All Mail pass by Message-ID — kills the INBOX/All-Mail duplication.
- Custom labels ride the message.new event; the labels plugin subscribes and maps
  them to chips as "<name> [Gmail]" (per-message + thread aggregate + known set),
  so labels fill in gradually with the sync window. Non-ASCII labels decode right.

Labels self-healing (message-driven reconcile):
- Per-message keys are the source of truth; t: aggregates and _labels are derived.
  Reconcile drops labels of deleted messages, regroups survivors by their current
  thread (fixing JWZ thread merges), rewrites changed t: keys, and rebuilds _labels
  from live messages — keeping user labels, dropping orphaned Gmail ones.
- New SDK reads: sdk.threads.existing / sdk.messages.threads_of. Sidebar refreshes
  live via a plugin.labels.changed WS event on new labels.

Account deletion: prune threads left empty after the cascade (they were user-scoped,
so only messages cascaded) + de-list the account from surviving cross-account threads.

Sync SPAM: opt-in per-account sync_spam (migration 0015, default off) — the engine
skips the Junk folder in backfill and poll unless enabled; wizard checkbox added.

Robustness / UX:
- WebSocket auto-reconnects with backoff and resyncs on (re)connect, and account
  add/delete invalidates threads/labels — no more hard refresh for live updates.
- Backfill banner + sidebar ring also require done < total, so a completed account
  can't leave a stuck "X of X".
- Scrub lone UTF-16 surrogates from parsed headers/bodies so bad messages no longer
  crash the backfill on Postgres text/JSONB.
- Ultimo signet logo in the Mail/Calendar/Contacts sidebar header (and at the top of
  the collapsed rail), via the shared plugin-ui.css + MailLayout.

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

frontend/src/routes/MailLayout.tsx

@@ -2,6 +2,7 @@ import { keepPreviousData, useMutation, useQuery, useQueryClient } from "@tansta
 import { useEffect, useRef, useState } from "react";
 import { Link, useMatch, useNavigate, useSearchParams } from "react-router-dom";
 
+import signetLogo from "../../icons/ultimo-logo-signet.svg";
 import { AppSwitcher } from "../components/AppSwitcher";
 import { Composer, type ComposerInit, draftToInit } from "../components/compose/Composer";
 import { DraftsList } from "../components/list/DraftsList";
@@ -512,7 +513,14 @@ export function MailLayout() {
             collapsed ? "flex-col items-center gap-1 px-2" : "items-center justify-between px-3"
           }`}
         >
-          {!collapsed && <AppSwitcher />}
+          {collapsed ? (
+            <img src={signetLogo} alt="Ultimo" className="h-7 w-auto shrink-0" />
+          ) : (
+            <div className="flex items-center gap-2">
+              <img src={signetLogo} alt="Ultimo" className="h-7 w-auto shrink-0" />
+              <AppSwitcher />
+            </div>
+          )}
           <div className={`flex items-center gap-1 ${collapsed ? "flex-col" : ""}`}>
             <button
               onClick={() => setCollapsed((v) => !v)}
@@ -573,7 +581,11 @@ export function MailLayout() {
                 >
                   <AccountDot
                     color={a.color}
-                    syncing={a.state === "backfilling" && a.backfill_total > 0}
+                    syncing={
+                      a.state === "backfilling" &&
+                      a.backfill_total > 0 &&
+                      a.backfill_done < a.backfill_total
+                    }
                     total={a.backfill_total}
                     done={a.backfill_done}
                   />