Fix: sync username to persistent state on auth verification

The username was stored in /tmp/assa-auth-state.json but not synced to
~/.config/assa/state.json when auth was verified from cache. This caused
x_conversations to fail with "I need your X username" even though auth
was successful.

Now verifyCachedAuth() calls setPersistentUsername() to ensure the
username is always synced to the persistent state file.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: nearestnabors

src/arcade/client.ts

@@ -313,6 +313,8 @@ async function verifyCachedAuth(): Promise<{
   try {
     await executeTool("X.LookupSingleUserByUsername", { username: "x" });
     log("Auth verified, using cached username:", `@${authenticatedUsername}`);
+    // Sync username to persistent state (in case it wasn't saved before)
+    setPersistentUsername(authenticatedUsername);
     return { authorized: true, username: authenticatedUsername };
   } catch (error) {
     log(