Clear current username during watch interval wait to prevent misleading UI

When using --watch-with-interval, clear the current user from StatusExchange
before starting the wait period between processing cycles. This prevents the
WebUI from displaying a username during the wait, which could mislead users
into thinking a specific user is still being processed.

**Change:**
- Add clear_current_user() call before watch interval wait in run_with_configs()
- Add explanatory comment about UI clarity

**User Experience:**
- Before: WebUI showed last processed user during wait periods
- After: WebUI shows no current user during wait, correctly indicating idle state

🤖 Generated with [Claude Code](https://claude.ai/code)

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

Author: AndreyNikiforov

src/icloudpd/base.py

@@ -253,6 +253,8 @@ def run_with_configs(global_config: GlobalConfig, user_configs: Sequence[UserCon
                     return 0
 
             # Wait for the watch interval before next iteration
+            # Clear current user during wait period to avoid misleading UI
+            shared_status_exchange.clear_current_user()
             logger.info(f"Waiting for {watch_interval} sec...")
             interval: Sequence[int] = range(1, watch_interval)
             iterable: Sequence[int] = (