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.Headless/Plugins/HeadlessPluginHost.cs

@@ -99,6 +99,25 @@ internal sealed class HeadlessPluginHost
         }
     }
 
+    /// <summary>
+    /// Campaign QT slice QT6. Same borrow-don't-own shape as
+    /// <see cref="Entities"/>: projected from the canonical tracker on read.
+    /// Names and status text are empty here — a headless host has no dat
+    /// access — while every numeric field a bot actually branches on
+    /// (contract id, stage, progress) is present.
+    /// </summary>
+    public IReadOnlyList<ContractSnapshot> Contracts
+    {
+        get
+        {
+            ObjectDisposedException.ThrowIf(_disposed, this);
+            return AcDream.Runtime.Gameplay.ContractPluginProjection.Project(
+                _runtime.ContractsOwner.View,
+                catalog: null,
+                now: DateTime.UtcNow);
+        }
+    }
+
     public event Action<WorldEntitySnapshot> EntitySpawned
     {
         add