Stop a letter key firing another letter's shortcut on non-QWERTY layouts #2662

Part of #2422 (F-DSK). Found by the independent review of #2661. This is existing v2 behaviour.

admin.js matches a letter shortcut by the character typed or by its physical key (event.code). On a layout where the physical key types a different letter, one letter fires another letter's shortcut:

• On French AZERTY, the key that types "q" sits where QWERTY has A, so typing "q" approves the set. The review confirmed this with a simulated keypress.
• On Dvorak, "l" publishes and "o" submits.

An approval can't be undone, so this is severe on any non-QWERTY Latin layout.

Scope

• A shortcut matches by its physical key only when the key typed is not a Latin letter or digit. A Persian or Hebrew layout keeps working, and a key that types another Latin letter never fires a different shortcut.
• Tests: an AZERTY "q" and a Dvorak "l" don't act, and a Persian key on A's position still approves.

Acceptance

• No key that types one Latin letter fires another letter's shortcut.