feat: add "Always Show Overlay" setting to keep tool status labels permanently visible #106
Description
What problem does this solve?
Currently, the tool status overlay (the activity label shown above a character) only appears when hovering over or selecting an agent. This makes it hard to monitor agent activity at a glance without hovering over each character individually.
Proposed solution
Add an "Always Show Overlay" toggle in the Settings modal. When enabled, the tool status label is permanently visible above all agents — no hover required. When disabled, the existing hover-only behavior is preserved.
Where it fits
This is a non-breaking UX improvement. The setting is local to the webview session (no persistence needed) and follows the existing pattern used by the "Debug Mode" toggle in Settings.