Gate every share entry point on login, de-duplicate the share-link and
color-identity logic behind DeckShareUtils and an injected querier, and
replace the silent tray/status-bar notices with always-visible dialogs.
- abstract_tab_deck_editor: explain that sharing requires a connection
instead of silently doing nothing when logged out
- tab_deck_storage: disable the share action on disconnect, reject
folder/deck mixes and the root folder with clear warnings, re-enable
Create on every entry/response so a dropped connection cannot leave
the button disabled
- tab_deck_storage_visual: same login gate for the context-menu entry,
visible success/error dialogs, and a symmetric in-flight guard
- getDeckColorIdentity now takes a CardDatabaseQuerier, dropping the
CardDatabaseManager singleton access and enabling unit tests
