feat(hooks): add auto-update-checker for plugin version management

Checks npm registry for latest version on session.created, invalidates
cache and shows toast notification when update is available.

🤖 GENERATED WITH ASSISTANCE OF [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

src/hooks/auto-update-checker/cache.ts

@@ -0,0 +1,18 @@
+import * as fs from "node:fs"
+import { VERSION_FILE } from "./constants"
+import { log } from "../../shared/logger"
+
+export function invalidateCache(): boolean {
+  try {
+    if (fs.existsSync(VERSION_FILE)) {
+      fs.unlinkSync(VERSION_FILE)
+      log(`[auto-update-checker] Cache invalidated: ${VERSION_FILE}`)
+      return true
+    }
+    log("[auto-update-checker] Version file not found, nothing to invalidate")
+    return false
+  } catch (err) {
+    log("[auto-update-checker] Failed to invalidate cache:", err)
+    return false
+  }
+}