[Feature] UX discoverability with focus/hover

**Summary:** Improve UX discoverability with focus/hover action descriptions.
## 1) Hover / focus descriptions for buttons

### Problem

Icon-only or compact buttons are ambiguous; users want discoverability without reading the wiki.

### Recommended implementation

- **Primary:** On **focus**, show a one-line description in a **status bar** or **help line** (keyboard-first; works in all terminals).
- **Secondary:** If mouse tracking is enabled and supported, mirror the same string on **hover** after a short debounce.
- Centralize metadata: extend button/widget definitions with `label_short`, `description`, optional `keybind_hint` so help overlay and inline hints stay in sync.

### Acceptance criteria

- Every actionable control in main flows has a description visible via focus or documented alternative.
- No duplicate strings diverging from help overlay.

### Testing

- Snapshot or unit test that button registry includes non-empty descriptions for registered actions.

Locate the button or widget registry, help overlay, and status-bar or help-line entry points mentioned in the issue, then inspect how actionable controls are defined and tested. Verify whether mouse tracking and snapshot or unit-test conventions already exist. Done means main-flow controls expose non-empty descriptions through focus or the documented alternative, with shared text and registry coverage.

Written by the indexing model from the issue text.