feat: add copy identifier shortcut

[Green00101]

Description

Adds a keyboard shortcut (Ctrl + Shift + C, Option + Shift + C on macOS) to copy the current entity identifier.

• The shortcut is registered inside the CopyIdentifier component, so all pages with a copy identifier button support it and the copied value is identical to the button's output.
• A notification is shown after copying; the shortcut is documented in the button tooltip. Mouse interactions are unchanged.
• Also added a "Copy identifier" entry in the Edit menu.

Closes #761

Note before testing

macOS was not tested, because I don't have a Mac device.

Tests to perform

1. On each database page with a copy identifier button (Pokémon, Moves, Items...), press Ctrl + Shift + C: a single success notification appears and the clipboard contains the identifier with the : prefix (e.g. :bulbasaur), identical to the copy button output.
2. On the Texts and Maps pages, the shortcut copies the id without the : prefix.
3. Hover the copy button: the tooltip shows the shortcut; clicking it still works as before.
4. Switch entity (Ctrl + Left/Right) then press the shortcut: the new entity's identifier is copied.
5. On pages without a copy identifier button, the shortcut does nothing.

These are the tests I performed. Please let me know if there are any additional cases I should check.