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>

services/mana-auth/src/auth/better-auth.config.ts

@@ -266,7 +266,7 @@ export function createBetterAuth(databaseUrl: string) {
 			'https://element.mana.how',
 			'https://inventar.mana.how',
 			'https://link.mana.how',
-			'https://manadeck.mana.how',
+			'https://cards.mana.how',
 			'https://matrix.mana.how',
 			'https://mchat.mana.how',
 			'https://mukke.mana.how',