fix: re-export EasyInputMessageContentInputImage, OutputInputImage, and OpenAIResponsesToolChoiceUnion

These SDK types were used internally but not re-exported, forcing
consumers to add a direct @openrouter/sdk dependency to access them.

Author: mattapperson

.changeset/export-missing-image-toolchoice-types.md

@@ -0,0 +1,5 @@
+---
+"@openrouter/agent": patch
+---
+
+Re-export `EasyInputMessageContentInputImage`, `OutputInputImage`, and `OpenAIResponsesToolChoiceUnion` from `@openrouter/sdk/models` so consumers can use these types without a direct SDK dependency.

src/index.ts

@@ -10,6 +10,7 @@ export type {
   ChatAssistantMessage,
   ChatMessages,
   EasyInputMessage,
+  EasyInputMessageContentInputImage,
   EasyInputMessageContentUnion1,
   EasyInputMessageRoleUnion,
   // Error event
@@ -24,7 +25,9 @@ export type {
   InputsUnion,
   InputText,
   InputVideo,
+  OpenAIResponsesToolChoiceUnion,
   OpenResponsesResult,
+  OutputInputImage,
   // Output item types (StreamableOutputItem members)
   OutputFileSearchCallItem,
   OutputFunctionCallItem,