/clear should reset mode to defaultMode instead of preserving previous mode

Problem

After running /clear, the current mode (e.g., acceptEdits) is preserved from the previous session state. This is unexpected — /clear is meant to start fresh, but the mode setting carries over.

Expected Behavior

After /clear, the mode should reset to the value configured in defaultMode (e.g., plan).

Current Behavior

If the user was in acceptEdits mode before /clear, they remain in acceptEdits mode after /clear, ignoring the defaultMode setting.

Workaround

None available via hooks — /clear does not trigger any hook events, so there's no way to intercept and reset the mode programmatically.

Suggested Fix

When /clear executes, reset the active mode to the value of defaultMode from settings.