refactor(ralph-loop): split hook into state controller and event handler modules

Extract Ralph loop lifecycle management:
- loop-state-controller.ts: start/stop/recovery state machine
- ralph-loop-event-handler.ts: event handling logic
- continuation-prompt-builder.ts, continuation-prompt-injector.ts
- completion-promise-detector.ts, loop-session-recovery.ts
- message-storage-directory.ts

src/hooks/ralph-loop/message-storage-directory.ts

@@ -0,0 +1,16 @@
+import { existsSync, readdirSync } from "node:fs"
+import { join } from "node:path"
+import { MESSAGE_STORAGE } from "../../features/hook-message-injector"
+
+export function getMessageDir(sessionID: string): string | null {
+	if (!existsSync(MESSAGE_STORAGE)) return null
+
+	const directPath = join(MESSAGE_STORAGE, sessionID)
+	if (existsSync(directPath)) return directPath
+
+	for (const dir of readdirSync(MESSAGE_STORAGE)) {
+		const sessionPath = join(MESSAGE_STORAGE, dir, sessionID)
+		if (existsSync(sessionPath)) return sessionPath
+	}
+	return null
+}