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>

.prettierignore

@@ -69,8 +69,8 @@ packages/shared-landing-ui/src/sections/TestimonialSection.astro
 **/*ANDROID*.md
 **/*IOS*.md
 apps/chat/FEATURE_REQUIREMENTS.md
-apps/manadeck/CI_CD_SETUP_GUIDE.md
-apps/manadeck/MANA_CORE_INTEGRATION_CHECKLIST.md
+apps/cards/CI_CD_SETUP_GUIDE.md
+apps/cards/MANA_CORE_INTEGRATION_CHECKLIST.md
 apps/picture/DEPLOYMENT_COMPLETE.md
 apps/zitare/apps/web/THEMING.md
 BACKEND_DESIGN_PATTERN_AUDIT.md