feat: quick actions on email rows (read/unread, star, trash)

- EmailRow shared component with hover action buttons: mark read/unread, star/unstar, trash
- Optimistic UI — local state patches immediately on click; row fades and becomes non-interactive during the API call
- Trashed rows disappear from the current folder view via onRemove callback
- Backend: EmailController single-email endpoints (POST /email/{id}/read|unread|star|unstar|trash|untrash)
- Star/Unstar added to CleanupActionType enum and CleanupService (maps to STARRED Gmail label via BatchModifyAsync)
- UserId scope enforced in ResolveTargetsAsync — a user can only act on their own emails
- action buttons use stopPropagation so clicking them does not open Gmail

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

src/InboxIntel.Api/Controllers/EmailController.cs

@@ -0,0 +1,44 @@
+using InboxIntel.Application.Abstractions;
+using InboxIntel.Application.DTOs;
+using InboxIntel.Domain.Enums;
+using Microsoft.AspNetCore.Mvc;
+
+namespace InboxIntel.Api.Controllers;
+
+/// <summary>
+/// Single-email quick actions. All writes are scoped to the authenticated user's
+/// UserId so one user cannot mutate another user's email.
+/// Read/star are non-destructive and execute without confirmation.
+/// Trash is reversible and also executes without a separate confirm step —
+/// the single-email context makes the intent unambiguous.
+/// </summary>
+public class EmailController : ApiControllerBase
+{
+    private readonly ICleanupService _cleanup;
+    public EmailController(ICleanupService cleanup) => _cleanup = cleanup;
+
+    [HttpPost("{id:guid}/read")]
+    public Task<IActionResult> MarkRead(Guid id, CancellationToken ct) => Act(id, CleanupActionType.MarkRead, ct);
+
+    [HttpPost("{id:guid}/unread")]
+    public Task<IActionResult> MarkUnread(Guid id, CancellationToken ct) => Act(id, CleanupActionType.MarkUnread, ct);
+
+    [HttpPost("{id:guid}/star")]
+    public Task<IActionResult> Star(Guid id, CancellationToken ct) => Act(id, CleanupActionType.Star, ct);
+
+    [HttpPost("{id:guid}/unstar")]
+    public Task<IActionResult> Unstar(Guid id, CancellationToken ct) => Act(id, CleanupActionType.Unstar, ct);
+
+    [HttpPost("{id:guid}/trash")]
+    public Task<IActionResult> Trash(Guid id, CancellationToken ct) => Act(id, CleanupActionType.Trash, ct);
+
+    [HttpPost("{id:guid}/untrash")]
+    public Task<IActionResult> Untrash(Guid id, CancellationToken ct) => Act(id, CleanupActionType.Archive, ct);
+
+    private async Task<IActionResult> Act(Guid id, CleanupActionType action, CancellationToken ct)
+    {
+        var req = new CleanupRequestDto(action, new[] { id }, null, null, Confirmed: true);
+        var result = await _cleanup.ExecuteAsync(UserId, req, ct);
+        return result.Succeeded ? Ok() : BadRequest(new { error = result.Error });
+    }
+}