Merge remote-tracking branch 'origin/worktree/web-multimodal-image-input' into worktree/pr555-simplify

# Conflicts:
#	.agents/notes/implemented/feature/2026-07-22-web-multimodal-image-input-and-durable-attachments.i18n.yaml
#	apps/web/tests/image-display.snapshot.ts
#	docs/core-data-structures/core.i18n.yaml
#	packages/client/ui-trajectory/tests/client-bundle.spec.ts

docs/core-data-structures/core.md

@@ -481,7 +481,10 @@ type AgentCancelCause =
 `Agent` is an interface over the public live-agent contract. Concrete drivers own the `followup`/`steer`/`inject` aliases and route them through `send`'s (`target` × `wakeup`) matrix.
 
 ```ts type-equiv
-/** Public live-agent handle with aliases over the unified delivery primitive. */
+/**
+ * Public live-agent handle with aliases over the unified delivery primitive.
+ * @typert object
+ */
 interface Agent {
   /** The single identity shared with {@link session}. */
   readonly id: SessionId