fix: correct task history slicing order for prompt navigation

Task history was using .slice(-100) which gets the newest 100 tasks,
but we want to show oldest tasks first when navigating. Changed to
.slice(0, 100) to get the oldest 100 tasks instead.

This ensures that when starting fresh (no conversation), up arrow
shows the oldest task prompts first, which is the intended behavior.

Author: hannesrudolph

webview-ui/src/components/chat/hooks/usePromptHistory.ts

@@ -91,8 +91,8 @@ export const usePromptHistory = ({
 				return item.task && item.task.trim() !== "" && (!item.workspace || item.workspace === cwd)
 			})
 			.map((item) => item.task)
-			// Limit history size to prevent memory issues
-			.slice(-MAX_PROMPT_HISTORY_SIZE)
+			// Limit history size to prevent memory issues - take oldest tasks first
+			.slice(0, MAX_PROMPT_HISTORY_SIZE)
 		// No reverse - keep chronological order so up arrow shows older tasks first
 
 		return taskPrompts