fix(categories): correct all 7 smart-folder bugs at source (PHASE 2) (#38)

src/InboxIntel.Api/Controllers/EmailController.cs

@@ -72,6 +72,22 @@ public class EmailController : ApiControllerBase
     [HttpPost("{id:guid}/untrash")]
     public Task<IActionResult> Untrash(Guid id, CancellationToken ct) => Act(id, CleanupActionType.Archive, ct);
 
+    /// <summary>Toggle the local-only Read Later marker (no Gmail side effect).</summary>
+    [HttpPost("{id:guid}/readlater")]
+    public Task<IActionResult> ReadLater(Guid id, CancellationToken ct) => SetReadLater(id, true, ct);
+
+    [HttpPost("{id:guid}/unreadlater")]
+    public Task<IActionResult> UnreadLater(Guid id, CancellationToken ct) => SetReadLater(id, false, ct);
+
+    private async Task<IActionResult> SetReadLater(Guid id, bool value, CancellationToken ct)
+    {
+        var email = await _db.Emails.FirstOrDefaultAsync(e => e.Id == id && e.UserId == UserId, ct);
+        if (email is null) return NotFound();
+        email.IsReadLater = value;
+        await _db.SaveChangesAsync(ct);
+        return Ok();
+    }
+
     /// <summary>
     /// Inline unsubscribe. Detects the unsubscribe mechanism for the email's sender,
     /// then executes it (HTTP one-click or HTTP link). mailto targets cannot be sent