feat(api): media detail + info + image-folder endpoints (#141/#161)

Add REST endpoints backing the SPA media detail pages and image browser:

- GET /api/movies/{id}, /api/shows/{id}, /api/seasons/{id}, /api/artists/{id}
  wrapping the existing detail queries; 404 on None.
- GET /api/media-items/{id}/info wrapping GetMediaItemInfo; UnableToLocateMediaItem
  -> 404, other errors -> 422.
- GET /api/images/folders?parentId= and PUT /api/images/folders/{id}/duration
  (validates null-or-positive -> 400; existence guard via new ImageFolderExists
  query -> 404).
- Extend GetLibraryBrowseItems parentId drill-in to Episode (episodes of a season,
  episode-number order) and MusicVideo (an artist's music videos, album/track order),
  alongside the existing TelevisionSeason branch.

Response DTOs live in ErsatzTV.Core/Api/* and never expose Application VMs. Artwork
values are rooted for the SPA via a shared ErsatzTV.Core/Api/ApiArtwork helper
(mirrors the #180/#181 browse-handler logic; handles jellyfin/emby proxy prefixes,
http passthrough, empty). Regenerated OpenAPI v1.json + web v1.d.ts. New controllers
registered in ApiControllerSecurityTests.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ErsatzTV/Controllers/Api/MoviesController.cs

@@ -0,0 +1,47 @@
+using ErsatzTV.Application.Movies;
+using ErsatzTV.Core.Api;
+using ErsatzTV.Core.Api.Media;
+using ErsatzTV.Core.Api.Movies;
+using ErsatzTV.Core.Domain;
+using ErsatzTV.Extensions;
+using MediatR;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ErsatzTV.Controllers.Api;
+
+[ApiController]
+public class MoviesController(IMediator mediator) : ControllerBase
+{
+    [HttpGet("/api/movies/{id:int}", Name = "GetMovieById")]
+    [Tags("Movies")]
+    [EndpointSummary("Get a movie by id")]
+    [EndpointGroupName("general")]
+    [ProducesResponseType(typeof(MovieDetailResponseModel), StatusCodes.Status200OK)]
+    [ProducesResponseType(typeof(ProblemDetails), StatusCodes.Status404NotFound)]
+    public async Task<IActionResult> GetById(int id, CancellationToken cancellationToken)
+    {
+        Option<MovieViewModel> result = await mediator.Send(new GetMovieById(id), cancellationToken);
+        return result.Map(vm => Project(id, vm)).ToGetResult();
+    }
+
+    private static MovieDetailResponseModel Project(int id, MovieViewModel vm) =>
+        new(
+            id,
+            vm.Title,
+            vm.Year,
+            vm.Plot,
+            vm.Genres,
+            vm.Tags,
+            vm.Studios,
+            vm.ContentRatings,
+            vm.Languages,
+            vm.Actors.Map(a => new ActorResponseModel(a.Id, a.Name, a.Role, ApiArtwork.Root(a.Thumb, ArtworkKind.Thumbnail))).ToList(),
+            vm.Directors,
+            vm.Writers,
+            vm.Path,
+            vm.LocalPath,
+            vm.MediaItemState,
+            ApiArtwork.Root(vm.Poster, ArtworkKind.Poster),
+            ApiArtwork.Root(vm.FanArt, ArtworkKind.FanArt));
+}