refactor: rename ManaDeck to Cards across entire monorepo

Rename the flashcard/deck management app from ManaDeck to Cards:
- Directory: apps/manadeck → apps/cards, packages/manadeck-database → packages/cards-database
- Packages: @manadeck/* → @cards/*, @manacore/manadeck-database → @manacore/cards-database
- Domain: manadeck.mana.how → cards.mana.how
- Storage: manadeck-storage → cards-storage
- Database: manadeck → cards
- All shared packages, infra configs, services, i18n, and docs updated
- 244 files changed, zero remaining manadeck references

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scripts/validate-monorepo.mjs

@@ -139,7 +139,7 @@ function checkWorkspaceProtocol(packagePath, packageJson) {
 		'@calendar/',
 		'@contacts/',
 		'@todo/',
-		'@manadeck/',
+		'@cards/',
 		'@zitare/',
 		'@voxel-lava/',
 		'@mana-games/',