This refactors the "Panel Button Clicked" telemetry event to fire from
`workspace.rs` instead of `dock.rs`.

Previously, the event was emitted in the `PanelButtons` render method's
click handler. Now it fires at the workspace level in two places:
- `toggle_dock()` - captures panel toggles via dock buttons
- `focus_panel<T>()` - captures panel focus via keyboard shortcuts

This ensures the telemetry fires once per user action regardless of
input method, and retrieves the panel name dynamically via
`persistent_name()` rather than relying on a pre-computed local
variable.

Release Notes:

- N/A