feat: add prompt opening behavior modes

frontend/src/components/pages/AssistantPage.tsx

@@ -179,6 +179,7 @@ function blankPromptForm(name: string): AssistantForm {
     turnConfig: defaultTurnConfig(),
     startup: {
       executionMode: "sequential",
+      openingMode: "interruptible",
       entryMode: "wait_user",
       actions: [],
       openingMessage: null,
@@ -473,6 +474,7 @@ export function AssistantPage(props: AssistantPageProps) {
       turnConfig: normalizeTurnConfig(a.turnConfig),
       startup: {
         executionMode: "sequential",
+        openingMode: a.startup?.openingMode ?? "interruptible",
         entryMode: a.startup?.entryMode ?? "wait_user",
         actions: a.startup?.actions ?? [],
         openingMessage: a.startup?.openingMessage ?? null,
@@ -548,6 +550,7 @@ export function AssistantPage(props: AssistantPageProps) {
       turnConfig: defaultTurnConfig(),
       startup: {
         executionMode: "sequential",
+        openingMode: "interruptible",
         entryMode: "wait_user",
         actions: [],
         openingMessage: null,