feat(quest): QT6 — plugins can read the contract tracker

The last piece of QT6's own scope: r10-quest-dialogs.md §11.6's contract half.
IGameState.Contracts exposes what the client structurally knows about quests,
which — per that same research — is the tracker and nothing else. The rest of
§11.6 (chat stream, tells, give, use, confirmations) is other features and
stays out of this campaign.

A pull-through source rather than a pushed mirror. Contracts change rarely and
are already owned canonically, so a second copy would only be a thing to keep
in step; reading through means a plugin cannot observe a stale list.

Both hosts implement it. The headless one carries contract id, stage and
progress but no names — a bot has no dat access — because losing the TEXT is
expected while losing the QUEST would leave a bot silently unable to see what
it is on. Same rule covers a contract the installed dat has never heard of: it
still projects, with empty text and a correct status, rather than vanishing.

The interface member is defaulted so a host predating this campaign still
satisfies IGameState.

Two lazy catalog loads exist (the panel's and this one) rather than one shared
instance. That is deliberate: threading a shared ContractCatalog through three
composition records to avoid reading a 322-row immutable table at most twice
per session would be plumbing for no correctness or performance gain, and the
comment at the call site says so.

Campaign QT is complete; the connected user gate is owed.

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

src/AcDream.Runtime/Gameplay/ContractPluginProjection.cs

@@ -0,0 +1,59 @@
+using System;
+using System.Collections.Generic;
+using AcDream.Core.Net.Messages;
+using AcDream.Core.Quests;
+using AcDream.Plugin.Abstractions;
+
+namespace AcDream.Runtime.Gameplay;
+
+/// <summary>
+/// Projects the canonical contract tracker into the plugin-facing
+/// <see cref="ContractSnapshot"/> shape.
+/// </summary>
+/// <remarks>
+/// Lives here rather than in either host because both of them need it and
+/// neither owns the tracker. The authored catalog is optional: a headless bot
+/// has no dat access, and a contract the installed dat has never heard of still
+/// has to appear — a plugin must not silently miss a live quest because the
+/// text for it is unavailable.
+/// </remarks>
+public static class ContractPluginProjection
+{
+    public static IReadOnlyList<ContractSnapshot> Project(
+        IRuntimeContractView contracts,
+        ContractCatalog? catalog,
+        DateTime now)
+    {
+        ArgumentNullException.ThrowIfNull(contracts);
+
+        IReadOnlyList<ContractTracker> tracked = contracts.GetContracts();
+        if (tracked.Count == 0)
+            return [];
+
+        uint displayed = contracts.Snapshot.DisplayContractId;
+        var result = new ContractSnapshot[tracked.Count];
+        for (int i = 0; i < tracked.Count; i++)
+        {
+            ContractTracker tracker = tracked[i];
+            ContractEntry? entry = catalog?.Lookup(tracker.ContractId);
+
+            result[i] = new ContractSnapshot(
+                tracker.ContractId,
+                (uint)tracker.Stage,
+                tracker.Progress,
+                tracker.ContractId == displayed,
+                entry?.ContractName ?? string.Empty,
+                entry?.Description ?? string.Empty,
+                entry is null
+                    ? string.Empty
+                    : ContractProgressText.Build(
+                        (uint)tracker.Stage,
+                        tracker.TimeWhenRepeats,
+                        tracker.ReceivedAt,
+                        entry,
+                        now));
+        }
+
+        return result;
+    }
+}