Fix action bar and buff bar spell tooltips showing 'Spell #xxx'

The action bar's inline Spell.dbc loader had a broken field index lookup:
operator[] on the layout map would silently insert 0 if 'Name' wasn't a
key, causing all names to be read from field 0 (the spell ID). Also the
once-only 'attempted' flag meant if assetMgr wasn't ready, it never retried.

Replace the duplicated broken DBC loading in the action bar and buff bar
with SpellbookScreen::lookupSpellName(), which reuses the spellbook's
already-correct loading (expansion layout + WotLK fallback). Remove the
now-unused actionSpellNames/actionSpellDbAttempted/actionSpellDbLoaded fields.

src/ui/spellbook_screen.cpp

@@ -71,6 +71,15 @@ void SpellbookScreen::loadSpellDBC(pipeline::AssetManager* assetManager) {
     dbcLoaded = !spellData.empty();
 }
 
+std::string SpellbookScreen::lookupSpellName(uint32_t spellId, pipeline::AssetManager* assetManager) {
+    if (!dbcLoadAttempted) {
+        loadSpellDBC(assetManager);
+    }
+    auto it = spellData.find(spellId);
+    if (it != spellData.end()) return it->second.name;
+    return {};
+}
+
 void SpellbookScreen::loadSpellIconDBC(pipeline::AssetManager* assetManager) {
     if (iconDbLoaded) return;
     iconDbLoaded = true;