refactor(mode-prompts): migrate search prompt

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

packages/prompts-core/src/mode-prompts.ts

@@ -0,0 +1,7 @@
+import searchModePrompt from "../prompts/mode/search.md" with { type: "text" }
+
+export const SEARCH_MODE_PROMPT = stripFinalLineFeed(searchModePrompt)
+
+function stripFinalLineFeed(prompt: string): string {
+  return prompt.endsWith("\n") ? prompt.slice(0, -1) : prompt
+}