Add keyboard shortcut for deck description

In the deck overview, `Options` and `Custom Study` have keyboard shortcuts (`O` and `C`), but `Description` does not.

Deck descriptions can serve as persistent deck-local documentation – e.g., to record conventions, sources, or other information that needs to be consulted or edited repeatedly. I use them extensively for this purpose, so mouse-only access makes the `Description` button less convenient than it could be.

`D` is already assigned to `Decks`. I suggest `I`, the first unassigned letter in `Description`.

I intend to submit a small PR adding the shortcut.

Start at the deck overview's existing Options and Custom Study keyboard-shortcut handling, then inspect how the Description button is opened. Add the proposed I shortcut while preserving D for Decks, and verify from the deck overview that pressing I opens Description.

Written by the indexing model from the issue text.