fix(messaging): a sent message no longer shows "Seen" instantly

Two independent defects; either alone caused it, in DMs, groups and channels.

1. useMessages reported a read of the newest NON-PENDING message regardless of
   author. Sending therefore made the client immediately mark its own message
   read, the server echoed a receipt for it, and the sender's bubble showed
   "Seen" before anyone had opened the thread. You do not read your own message:
   lastReadableId now skips your own.

2. The guard meant to catch exactly this — `e.actorId !== currentActorId` — could
   never fire: the receipt carries the reader's IIOS actor UUID while clients hold
   a userId, so the comparison was always true and every receipt, including your
   own, counted as the other side. The gateway now also emits userId on READ and
   DELIVERED receipts (matching what `annotation` already did), and ReceiptEvent
   carries it as optional so older servers still typecheck.

MockAdapter.markRead was a no-op, so it could not exercise any of this; it now
echoes a receipt like a real server. Regression test verified to fail without
the fix. SDK 0.1.14; suite 17 files / 101 tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packages/iios-kernel-client/src/types.ts

@@ -37,7 +37,11 @@ export interface OpenThreadResult {
 
 export interface ReceiptEvent {
   interactionId: string;
+  /** The reader's IIOS actor UUID — an internal id, NOT comparable to a caller's userId. */
   actorId: string;
+  /** The reader's userId — the same id space clients hold, so they can ignore their own receipt.
+   *  Optional: absent from servers older than the change that added it. */
+  userId?: string;
   kind: 'READ' | 'DELIVERED';
 }