v0.2: All videos folder, shared watched state, release-order sorting, official icon, OAuth plumbing, docs

- per-creator "All videos" folder (release order across sub-channels); sub-channel copies use
  cpost: ids and UserDataMirror keeps played/resume state in sync
- SortNameUpdater forces release-order sort names so every client lists newest first by default
- official Floatplane icon as channel image (Primary only — a channel Thumb hid video thumbnails
  in Continue Watching) and as 16:9 plugin thumbnail; one-time image replacement on upgrade
- OAuth device-flow login (FloatplaneAuthService + settings UI); needs a Floatplane client id;
  Turnstile verified domain-bound so password login inside Jellyfin is impossible
- generic install.sh (linuxserver / official image / native), thumb.png in package + manifest
- README rewritten for a general audience, doc/usage.md with screenshots, 60 tests

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

Jellyfin.Plugin.Floatplane/Channel/SortNameUpdater.cs

@@ -0,0 +1,120 @@
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using Jellyfin.Data.Enums;
+using MediaBrowser.Controller.Entities;
+using MediaBrowser.Controller.Library;
+using Microsoft.Extensions.Logging;
+
+namespace Jellyfin.Plugin.Floatplane.Channel;
+
+/// <summary>
+/// Every Jellyfin client lists a channel folder sorted by name by default, and the web
+/// client stores a sort choice per folder. To get release order without touching every
+/// folder, each video's <c>ForcedSortName</c> is set to its release time reversed
+/// (<c>(10^13 - unixMs)</c>, zero-padded), so "Name ascending" = newest first.
+/// Runs a few seconds after a listing (the items only exist in the database after
+/// Jellyfin has synced them) and during the scheduled refresh.
+/// </summary>
+public class SortNameUpdater
+{
+    private const long Epoch = 10_000_000_000_000; // > any unix ms this side of year 2286
+
+    private readonly ILibraryManager _libraryManager;
+    private readonly ILogger<SortNameUpdater> _logger;
+    private readonly SemaphoreSlim _gate = new(1, 1);
+    private int _scheduled;
+
+    public SortNameUpdater(ILibraryManager libraryManager, ILogger<SortNameUpdater> logger)
+    {
+        _libraryManager = libraryManager;
+        _logger = logger;
+    }
+
+    /// <summary>Sort name for a release date: newest first under ascending name order.</summary>
+    public static string SortNameFor(DateTime? releaseDate)
+    {
+        var ms = releaseDate.HasValue ? new DateTimeOffset(DateTime.SpecifyKind(releaseDate.Value, DateTimeKind.Utc)).ToUnixTimeMilliseconds() : 0;
+        return (Epoch - 1 - Math.Clamp(ms, 0, Epoch - 1)).ToString("D13", CultureInfo.InvariantCulture);
+    }
+
+    /// <summary>Schedules one pass shortly after a listing (coalesces bursts of calls).</summary>
+    public void ScheduleSoon()
+    {
+        if (Interlocked.CompareExchange(ref _scheduled, 1, 0) != 0)
+        {
+            return;
+        }
+
+        _ = Task.Run(async () =>
+        {
+            try
+            {
+                await Task.Delay(TimeSpan.FromSeconds(10)).ConfigureAwait(false);
+                Interlocked.Exchange(ref _scheduled, 0);
+                await UpdateAsync(CancellationToken.None).ConfigureAwait(false);
+            }
+            catch (Exception ex)
+            {
+                Interlocked.Exchange(ref _scheduled, 0);
+                _logger.LogWarning(ex, "Sort-name update failed");
+            }
+        });
+    }
+
+    /// <summary>Sets the forced sort name on every Floatplane video item that lacks the right one.</summary>
+    public async Task<int> UpdateAsync(CancellationToken ct)
+    {
+        await _gate.WaitAsync(ct).ConfigureAwait(false);
+        try
+        {
+            var channelIds = _libraryManager.GetItemList(new InternalItemsQuery
+            {
+                IncludeItemTypes = [BaseItemKind.Channel],
+                Name = "Floatplane"
+            }).Select(c => c.Id).ToArray();
+            if (channelIds.Length == 0)
+            {
+                return 0;
+            }
+
+            var items = _libraryManager.GetItemList(new InternalItemsQuery
+            {
+                ChannelIds = channelIds,
+                IncludeItemTypes = [BaseItemKind.Video],
+                Recursive = true
+            });
+
+            var changed = new List<BaseItem>();
+            foreach (var item in items)
+            {
+                if (FloatplaneChannel.PostIdOf(item.ExternalId) is null)
+                {
+                    continue;
+                }
+
+                var wanted = SortNameFor(item.PremiereDate ?? item.DateCreated);
+                if (!string.Equals(item.ForcedSortName, wanted, StringComparison.Ordinal))
+                {
+                    item.ForcedSortName = wanted;
+                    changed.Add(item);
+                }
+            }
+
+            if (changed.Count > 0)
+            {
+                await _libraryManager.UpdateItemsAsync(changed, changed[0].GetParent(), ItemUpdateType.MetadataEdit, ct).ConfigureAwait(false);
+                _logger.LogInformation("Set release-order sort names on {Count} Floatplane videos", changed.Count);
+            }
+
+            return changed.Count;
+        }
+        finally
+        {
+            _gate.Release();
+        }
+    }
+}