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>

docs/MANA_EARNING_SYSTEM.md

@@ -190,7 +190,7 @@ Ein User gilt als "verified" wenn MINDESTENS EINS zutrifft:
 
 ### Reward-Struktur
 
-#### ManaDeck
+#### Cards
 
 | Metrik | Threshold | Credits | Max/Monat |
 |--------|-----------|---------|-----------|
@@ -566,7 +566,7 @@ CREATE TABLE community.bounty_pool (
   - [ ] Create Admin endpoints für Manual Review Queue
 
 - [ ] **Integration in Content Apps**
-  - [ ] ManaDeck: Track deck copies
+  - [ ] Cards: Track deck copies
   - [ ] Zitare: Track quote submissions/views
   - [ ] Presi: Track template usage