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>

apps/cards/SETUP_GUIDE.md

@@ -1,4 +1,4 @@
-# Manadeck Setup Guide
+# Cards Setup Guide
 
 ## What's Been Completed
 
@@ -59,12 +59,12 @@ npm run start:dev
 # Sign up a test user
 curl -X POST http://localhost:8080/v1/auth/signup \
   -H "Content-Type: application/json" \
-  -d '{"email":"test@manadeck.com","password":"test123","username":"testuser"}'
+  -d '{"email":"test@cards.com","password":"test123","username":"testuser"}'
 
 # Sign in to get token
 curl -X POST http://localhost:8080/v1/auth/signin \
   -H "Content-Type: application/json" \
-  -d '{"email":"test@manadeck.com","password":"test123"}'
+  -d '{"email":"test@cards.com","password":"test123"}'
 
 # Copy the appToken from response
 export TOKEN="paste-your-token-here"