Problem

Every action in Scikit-Learner today requires a mouse click. Power users (and demos) suffer.

Proposal

Bind keyboard shortcuts for the most-used actions:

Implementation notes

• Single `keydown` listener at the document level in `frontend/js/app.js`.
• Skip when the focus is in a text input (`document.activeElement.tagName === 'INPUT' || 'TEXTAREA'`).
• A small "?" badge in the footer or top bar that opens a modal listing the shortcuts.

Acceptance criteria

• Each shortcut triggers the corresponding action.
• Shortcuts do not fire when typing in an input field.
• A discoverability hint (modal or tooltip) is visible from the UI.