[DeckShare] Address review findings and harden the share flows

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

cockatrice/src/interface/widgets/cards/additional_info/deck_color_identity.cpp

@@ -1,11 +1,11 @@
 #include "deck_color_identity.h"
 
 #include <QSet>
-#include <libcockatrice/card/database/card_database_manager.h>
+#include <libcockatrice/card/database/card_database_querier.h>
 #include <libcockatrice/deck_list/deck_list.h>
 #include <libcockatrice/deck_list/tree/inner_deck_list_node.h>
 
-QString getDeckColorIdentity(const DeckList &deck)
+QString getDeckColorIdentity(const DeckList &deck, const CardDatabaseQuerier *db)
 {
     const QStringList cardList = deck.getCardList({DECK_ZONE_MAIN, DECK_ZONE_SIDE});
     if (cardList.isEmpty()) {
@@ -15,7 +15,7 @@ QString getDeckColorIdentity(const DeckList &deck)
     QSet<QChar> colorSet; // A set to collect unique color symbols (e.g., W, U, B, R, G)
 
     for (const QString &cardName : cardList) {
-        CardInfoPtr currentCard = CardDatabaseManager::query()->getCardInfo(cardName);
+        CardInfoPtr currentCard = db->getCardInfo(cardName);
         if (currentCard) {
             const QString colors = currentCard->getColors(); // returns something like "WUB"
             for (const QChar &color : colors) {

cockatrice/src/interface/widgets/cards/additional_info/deck_color_identity.h

@@ -3,6 +3,7 @@
 
 #include <QString>
 
+class CardDatabaseQuerier;
 class DeckList;
 
 /**
@@ -11,7 +12,9 @@ class DeckList;
  *
  * Shared as a free function so the deck storage previews and the deck share
  * dialog compute identities identically.
+ *
+ * @param db Card database used to look up card color symbols.
  */
-QString getDeckColorIdentity(const DeckList &deck);
+QString getDeckColorIdentity(const DeckList &deck, const CardDatabaseQuerier *db);
 
 #endif // COCKATRICE_DECK_COLOR_IDENTITY_H