M2: Meili search + saved searches, sync windows + backfill progress, threading & image fixes

Search:
- Meilisearch backend (app/search/meili.py) + factory wiring; pinned SDK 2.7
- Search-as-you-type: debounced query + Postgres prefix matching, built from
  the DB tokenizer so full email addresses match (email stays one lexeme)
- Saved searches API + sidebar virtual mailboxes; save affordance in the box

Account sync windows (SPEC §12 M2):
- Choose at setup: All (recent 30d first, then remainder), Last 3 months, New only
- Per-account sync_window + "Sync remaining mail" from settings (idempotent re-run)
- Provider windowed backfill (SINCE/BEFORE), message_count, newest_uid
- migration 0012: accounts.sync_window + backfill_total/backfill_done

Backfill progress UX:
- Floating progress card (auto-dissolves after 10s) + spinning sidebar ring that
  fills with the account colour; driven by sync.progress over WS

Thread list pagination:
- Server-side offset + accurate grand total, with filter/order in SQL; working
  prev/next across all synced mail

Reading panel:
- "Load images" one-off now actually renders images (?images=1) without trusting
  the sender; envelope carries images_allowed so a trusted sender shows no prompt

Threading:
- Subject fallback no longer merges messages that declare an explicit (different)
  parent; true siblings still group via a shared-parent reference match. Fixes
  unrelated auto-replies with the same subject landing in one thread

Backend 257 tests green, ruff + mypy --strict clean; frontend tsc/eslint/vitest clean.

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

frontend/src/routes/wizard/AccountWizard.tsx

@@ -4,7 +4,7 @@ import { useNavigate } from "react-router-dom";
 
 import { useT } from "../../i18n";
 import { api, ApiError } from "../../lib/api";
-import type { ServerConfig } from "../../lib/types";
+import type { ServerConfig, SyncWindow } from "../../lib/types";
 
 const PALETTE = ["#2563eb", "#16a34a", "#d4762a", "#9333ea", "#dc2626", "#0891b2"];
 const EMPTY: ServerConfig = { host: "", port: 993, tls: "ssl", auth: "password" };
@@ -22,6 +22,7 @@ export function AccountWizard() {
   const [imap, setImap] = useState<ServerConfig>(EMPTY);
   const [smtp, setSmtp] = useState<ServerConfig>({ ...EMPTY, port: 465 });
   const [source, setSource] = useState<string>("");
+  const [syncWindow, setSyncWindow] = useState<SyncWindow>("all");
   const [busy, setBusy] = useState(false);
   const [tested, setTested] = useState(false);
   const [error, setError] = useState("");
@@ -72,6 +73,7 @@ export function AccountWizard() {
         imap,
         smtp,
         password,
+        sync_window: syncWindow,
       });
       await queryClient.invalidateQueries({ queryKey: ["accounts"] });
       setStep(3);
@@ -180,6 +182,28 @@ export function AccountWizard() {
               />
             ))}
           </div>
+          <fieldset className="rounded-lg border border-app-border p-3">
+            <legend className="px-1 text-xs text-app-muted">{t("wizard.syncWindow")}</legend>
+            <div className="space-y-1">
+              {(["all", "3months", "new"] as const).map((w) => (
+                <label key={w} className="flex cursor-pointer items-start gap-2 text-sm">
+                  <input
+                    type="radio"
+                    name="sync-window"
+                    className="mt-1"
+                    checked={syncWindow === w}
+                    onChange={() => setSyncWindow(w)}
+                  />
+                  <span>
+                    <span className="font-medium">{t(`wizard.syncWindow.${w}`)}</span>
+                    <span className="block text-xs text-app-faint">
+                      {t(`wizard.syncWindow.${w}.hint`)}
+                    </span>
+                  </span>
+                </label>
+              ))}
+            </div>
+          </fieldset>
           {tested && <p className="text-sm text-emerald-500">{t("wizard.testOk")}</p>}
           <div className="flex gap-2">
             {!tested ? (