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.Core/Plugins/WorldGameState.cs

@@ -10,6 +10,19 @@ public sealed class WorldGameState : IGameState
 
     public IReadOnlyList<WorldEntitySnapshot> Entities => _entities;
 
+    /// <summary>
+    /// Where <see cref="Contracts"/> reads from. Set once by the host.
+    /// </summary>
+    /// <remarks>
+    /// A pull-through source rather than a pushed list: contracts change rarely
+    /// and are already owned canonically elsewhere, so mirroring them here
+    /// would add a second copy to keep in step for no gain.
+    /// </remarks>
+    public Func<IReadOnlyList<ContractSnapshot>>? ContractsSource { get; set; }
+
+    public IReadOnlyList<ContractSnapshot> Contracts =>
+        ContractsSource?.Invoke() ?? [];
+
     /// <summary>
     /// Publish the current projection for an entity. Re-hydration replaces the
     /// prior snapshot instead of turning the current-state API into history.