feat: sync status indicator, unsubscribe queue UI, email body preview

SyncStatus widget polls /sync/status and shows a live progress bar in
the topbar while syncing, or last-synced time / error otherwise.

Unsubscribe page reworked into a proper queue: status filter tabs
(All/Pending/Succeeded/Failed), select-all, sorted by volume, status
badges, and a result toast after processing.

GET /email/{id} returns full BodyText; Senders detail view fetches
and renders it instead of just the snippet.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/InboxIntel.Application/DTOs/EmailDtos.cs

@@ -18,6 +18,24 @@ public record EmailSummaryDto(
     bool HasListUnsubscribe,
     bool SupportsOneClick);
 
+/// <summary>Full single-email view, including body text, for the detail pane.</summary>
+public record EmailDetailDto(
+    Guid Id,
+    string GmailMessageId,
+    string? Subject,
+    string? Snippet,
+    string? BodyText,
+    string SenderAddress,
+    string? SenderDisplayName,
+    DateTimeOffset SentAtUtc,
+    bool IsUnread,
+    bool IsStarred,
+    bool HasAttachments,
+    long SizeEstimateBytes,
+    EmailCategory Category,
+    bool HasListUnsubscribe,
+    bool SupportsOneClick);
+
 public record SenderStatDto(
     Guid SenderId,
     string Address,