fix(ui): preserve draft across prompt history

Stop resetting history navigation on input so editing recalled entries doesn't wipe the bottom draft. Allow ArrowDown navigation while in history and persist the session draft only for fresh prompts.

packages/ui/src/components/prompt-input.tsx

@@ -135,7 +135,6 @@ export default function PromptInput(props: PromptInputProps) {
     instanceFolder: () => props.instanceFolder,
     prompt,
     setPrompt,
-    resetHistoryNavigation,
     getTextarea: () => textareaRef ?? null,
     instanceAgents,
     commands: () => getCommands(props.instanceId),
@@ -303,7 +302,6 @@ export default function PromptInput(props: PromptInputProps) {
     const nextValue = before + insertion + after
 
     setPrompt(nextValue)
-    resetHistoryNavigation()
     setShowPicker(false)
     setAtPosition(null)