Merge pull request #509 from hildebrandttk/feat/unified-mailbox-account-scope

Feat/unified mailbox account scope

Rework the sidebar "All accounts" into an account-bounded "Unified Mailbox"
by default, with cross-account merging as an opt-in (admin-gated) sub-option.
The standalone per-account "All Mail" virtual folder is folded into the unified
All mail / Unread / Starred entries.

Conflict resolution notes:
- stores/settings-store.ts: both main and this branch independently added a
  per-account default-identity (#507) migration at different versions (main v6,
  branch v7). Merged migration is version 7 using the refactored migrateSettings
  function; the unified-mailbox rework is guarded at `version < 7` so users who
  stopped at main's interim v6 identity bump still receive it, while the #507
  identity-map coercion stays at `version < 6` so their populated map is kept.
- stores/auth-store.ts: kept main's applyPreferredIdentity (superset with the
  pre-#507 legacy migration).
- stores/email-store.ts: removed the ALL_MAIL_MAILBOX_ID paths (folded into the
  unified views) while preserving main's plugin hooks (onSearchResults /
  onEmailsFetched); adopted advancedSearchCrossViewEmails for advanced cross-view
  search.
- components/settings/layout-settings.tsx: kept main's faviconUnreadBadge setting
  alongside the new unifiedCrossAccount toggle.
- integration/: union-merged the two independently-authored suites - branch suite
  is authoritative (matches new behavior) with main's shared-identity (#569) group
  infrastructure preserved.
- components/email/email-composer.tsx: dropped a duplicate data-testid attribute
  introduced by the auto-merge.

components/email/thread-list-item.tsx

@@ -2,7 +2,7 @@
 
 import React, { useCallback } from "react";
 import { formatDate, formatDateTime, stripInvisibleLeading } from "@/lib/utils";
-import { Email, ThreadGroup, ALL_MAIL_MAILBOX_ID } from "@/lib/jmap/types";
+import { Email, ThreadGroup } from "@/lib/jmap/types";
 import { cn } from "@/lib/utils";
 import { SelectableAvatar } from "@/components/email/selectable-avatar";
 import { Paperclip, Star, Pin, Circle, ChevronRight, ChevronDown, Loader2, MessageSquare, CheckSquare, Square, Reply, Forward, CalendarClock, Folder } from "lucide-react";
@@ -97,7 +97,7 @@ const SingleEmailItem = React.forwardRef<HTMLDivElement, SingleEmailItemProps>(
     const showAvatarsInJunk = useSettingsStore((state) => state.showAvatarsInJunk);
     const hideJunkAvatarImages = currentMailboxRole === 'junk' && !showAvatarsInJunk;
     // Show the originating folder in the aggregate "All …" views.
-    const showSourceFolder = (isUnifiedView || selectedMailbox === ALL_MAIL_MAILBOX_ID) && !!email.sourceFolder;
+    const showSourceFolder = isUnifiedView && !!email.sourceFolder;
     const getAccountById = useAccountStore((state) => state.getAccountById);
     const accountColor = email.accountId ? getAccountById(email.accountId)?.avatarColor : undefined;
     const isChecked = selectedEmailIds.has(email.id);
@@ -463,7 +463,7 @@ export const ThreadListItem = React.forwardRef<HTMLDivElement, ThreadListItemPro
       : null;
 
     const { selectedMailbox, mailboxes, selectedEmailIds, toggleEmailSelection, selectRangeEmails, clearSelection, isUnifiedView, unifiedRole } = useEmailStore();
-    const showSourceFolder = (isUnifiedView || selectedMailbox === ALL_MAIL_MAILBOX_ID) && !!latestEmail.sourceFolder;
+    const showSourceFolder = isUnifiedView && !!latestEmail.sourceFolder;
     const getAccountById = useAccountStore((state) => state.getAccountById);
     const threadAccountColor = latestEmail.accountId ? getAccountById(latestEmail.accountId)?.avatarColor : undefined;
     // In Sent/Drafts folders, show recipient instead of sender (which is always