feat: Smart Folders sidebar, category heatmap, sidebar counts API

- Replace plain activity heatmap with CategoryHeatmapWidget on dashboard
- Add collapsible Smart Folders sidebar with Favorites, Mailbox, Smart Folders sections
- Favorites: customisable pinned shortcuts (default: Inbox, Unread, Large, Old, Read Later); pin/unpin smart folders via buttons; persists to localStorage
- Mailbox section: 11 Gmail mailbox items with icons and live count badges
- Smart Folders section: 10 category folders sorted by count desc
- Live count badges via new GET /api/v1/analytics/sidebar-counts endpoint
- Backend: SidebarCountsDto, GetSidebarCountsAsync with label lookups for SENT/DRAFT/SPAM, size/age filters, EmailCategory mapping
- Sidebar collapses to icon-only; section states persist to localStorage

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

src/InboxIntel.Infrastructure/Analytics/AnalyticsService.cs

@@ -88,6 +88,19 @@ public class AnalyticsService : IAnalyticsService
             .ToList();
     }
 
+    public async Task<IReadOnlyList<CategoryHeatmapCellDto>> GetCategoryHeatmapAsync(Guid userId, CancellationToken ct = default)
+    {
+        var raw = await _db.Emails
+            .Where(e => e.UserId == userId)
+            .Select(e => new { e.SentAtUtc, e.Category })
+            .ToListAsync(ct);
+
+        return raw
+            .GroupBy(x => new { x.Category, Dow = (int)x.SentAtUtc.DayOfWeek })
+            .Select(g => new CategoryHeatmapCellDto(g.Key.Category.ToString(), g.Key.Dow, g.Count()))
+            .ToList();
+    }
+
     public async Task<IReadOnlyList<AttachmentBreakdownDto>> GetAttachmentBreakdownAsync(Guid userId, CancellationToken ct = default)
     {
         var raw = await _db.Attachments
@@ -115,6 +128,60 @@ public class AnalyticsService : IAnalyticsService
         _ => "other"
     };
 
+    public async Task<SidebarCountsDto> GetSidebarCountsAsync(Guid userId, CancellationToken ct = default)
+    {
+        var emails = _db.Emails.Where(e => e.UserId == userId);
+
+        var allMail = await emails.CountAsync(ct);
+        var inbox   = await emails.CountAsync(e => e.IsInInbox, ct);
+        var unread  = await emails.CountAsync(e => e.IsUnread, ct);
+        var starred = await emails.CountAsync(e => e.IsStarred, ct);
+        var trash   = await emails.CountAsync(e => e.IsTrashed, ct);
+        var large   = await emails.CountAsync(e => e.SizeEstimateBytes > 5_000_000, ct);
+        var cutoff  = DateTimeOffset.UtcNow.AddYears(-1);
+        var old     = await emails.CountAsync(e => e.SentAtUtc < cutoff, ct);
+
+        // Label-backed counts (SENT / DRAFT / SPAM are system Gmail labels)
+        async Task<int> LabelCount(string gmailId)
+        {
+            var labelId = await _db.Labels
+                .Where(l => l.UserId == userId && l.GmailLabelId == gmailId)
+                .Select(l => (Guid?)l.Id)
+                .FirstOrDefaultAsync(ct);
+            return labelId.HasValue
+                ? await _db.EmailLabels.CountAsync(el => el.LabelId == labelId.Value, ct)
+                : 0;
+        }
+
+        var sent   = await LabelCount("SENT");
+        var drafts = await LabelCount("DRAFT");
+        var spam   = await LabelCount("SPAM");
+
+        // Category → smart-folder slug mapping
+        var catCounts = await emails
+            .GroupBy(e => e.Category)
+            .Select(g => new { Cat = g.Key, N = g.Count() })
+            .ToListAsync(ct);
+
+        int Cat(EmailCategory c) => catCounts.FirstOrDefault(x => x.Cat == c)?.N ?? 0;
+
+        var smartFolders = new Dictionary<string, int>
+        {
+            ["automated"] = Cat(EmailCategory.Notification),
+            ["finance"]   = Cat(EmailCategory.Finance),
+            ["social"]    = Cat(EmailCategory.Social),
+            ["shopping"]  = Cat(EmailCategory.Promotional),
+            ["noreply"]   = 0,
+            ["gaming"]    = 0,
+            ["sales"]     = 0,
+            ["ridesharing"] = 0,
+            ["food"]      = 0,
+            ["wellness"]  = 0,
+        };
+
+        return new SidebarCountsDto(inbox, allMail, unread, starred, sent, drafts, trash, spam, large, old, smartFolders);
+    }
+
     public async Task RefreshAggregatesAsync(Guid userId, CancellationToken ct = default)
     {
         var since = DateTimeOffset.UtcNow.AddDays(-365);